Methods, apparatuses and systems for supporting multi-user transmissions in a wireless local area network (wlan) system

ABSTRACT

Methods, devices and systems are provided for performing for multi-user (MU) transmission. A wireless transmit/receive unit (WTRU) may be configured to receive a frame, decode the received frame and determine whether the received frame is a null data packet (NDP) multi-user (MU) media access control (MAC) physical layer convergence protocol (PLCP) protocol data unit (PPDU) (NDP MU MAC PPDU) based on meeting an NDP condition. The NDP MU MAC PPDU may correspond to an MU transmission and may include a PLCP header which includes an NDP signal (SIG) field having MU control information. Based on the received frame meeting the NDP condition, the WTRU may be further configured to process the NDP SIG field, generate a response based on the NDP SIG field and the MU control information, and transmit the response.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.17/728,148, filed Apr. 25, 2022, which is a continuation of U.S. patentapplication Ser. No. 16/433,239, filed Jun. 6, 2019, which issued asU.S. Pat. No. 11,317,436 on Apr. 26, 2022, which is a continuation ofU.S. patent application Ser. No. 15/541,643, filed Jul. 5, 2017, whichis the U.S. National Stage, under 35 U.S.C. § 371, of InternationalApplication No. PCT/US2016/012642, filed Jan. 8, 2016, which claims thebenefit of U.S. Provisional Application No. 62/101,890, filed Jan. 9,2015, and U.S. Provisional Application No. 62/129,469, filed Mar. 6,2015, the contents of which are hereby incorporated by reference herein.

BACKGROUND

A wireless local area network (WLAN) in infrastructure basic service set(BSS) mode has an access point (AP) for the BSS and one or more stations(STAs) associated with the AP. The AP may have access to, or be able tointerface with, a distribution system (DS) or other type of wired orwireless network that carries traffic in and out of the BSS. Traffic toSTAs that originates from outside the BSS may arrive through the AP andbe delivered to the STAs. Traffic originating from STAs to destinationsoutside the BSS may be sent to the AP to be delivered to the respectivedestinations. Traffic between STAs within the BSS may also be sentthrough the AP or may be sent directly between the source anddestination STAs with a direct link setup (DLS), using, for example, anInstitute of Electrical and Electronics Engineers (IEEE) 802.11e DLS oran IEEE 802.11z tunneled DLS (TDLS). For example, a WLAN in independentBSS mode may have no AP, and, thus, STAs may communicate directly witheach other.

WLANs with very high throughput (VHT) of greater than 100 megabits persecond (Mbps) on top of the medium access control (MAC) layer are beingconsidered. To enhance system performance and achieve high data rates,VHT WLANs may include features, such as wideband transmissions, byaggregating channels. For example, in IEEE 802.11, a channel istypically 20 MHz wide, and four such 20 MHz channels may be aggregatedfor an 80 MHz wideband transmission. Typically, a BSS operates with a 20MHz channel as the primary channel on which the devices (AP and STAs) ofthe BSS camp. In order for a device (e.g., an AP or a STA) to make awideband transmission, it may need to aggregate one or more non-primary20 MHz channels with the primary 20 MHz channel to make up the desiredbandwidth to support the wideband transmission.

IEEE 802.11ac introduced a group identifier (ID) concept, which is usedfor downlink (DL) multi-user (MU) multiple-input/multiple-output (MIMO)(MU-MIMO) transmissions to enable the AP to address a group of STAs witha single group ID. However, the IEEE 802.11ac multi-user groupingmechanism cannot support large numbers of clusters for multiple MUtransmission schemes, a combination of orthogonal frequency-divisionmultiple access (OFDMA) clusters and orthogonal frequency-divisionmultiplexing (OFDM) MU-MIMO groups, or flexible clustering andscheduling mechanisms which may enable the per-transmission clusteringand scheduling. Furthermore, current MU control frames are overhead anddecrease MAC efficiency.

SUMMARY

Methods, apparatuses and systems for multi-user transmission aredescribed. A wireless transmit/receive unit (WTRU) may include areceiver, a transmitter and at least one processor, and may beconfigured to receive a frame, decode the received frame and determinewhether the received frame is a null data packet (NDP) multi-user (MU)media access control (MAC) physical layer convergence protocol (PLCP)protocol data unit (PPDU) (NDP MU MAC PPDU) based on meeting an NDPcondition. The NDP MU MAC PPDU may correspond to an MU transmission andmay include a PLCP header which includes an NDP signal (SIG) fieldhaving MU control information. Based on the received frame meeting theNDP condition, the WTRU may be further configured to process the NDP SIGfield, generate a response based on the NDP SIG field and the MU controlinformation, and transmit the response.

In another example, the WTRU may be configured to receive a null datapacket (NDP) multi-user (MU) media access control (MAC) physical layerconvergence protocol (PLCP) protocol data unit (PPDU) (NDP MU MAC PPDU)related to an MU transmission. The NDP MU MAC PPDU may include a PLCPheader which includes an NDP signal (SIG) field having MU controlinformation and the NDP SIG field may indicate a NDP MAC frame type ofthe NDP MU MAC PPDU. The WTRU may be configured to determine the NDP MACframe type from the NDP SIG field and generate a response based on thedetermined NDP MAC frame type and the MU control information.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding may be had from the following description,given by way of example in conjunction with the accompanying drawingswherein:

FIG. 1A is a system diagram of an example communications system in whichone or more disclosed embodiments may be implemented;

FIG. 1B is a system diagram of an example wireless transmit/receive unit(WTRU) that may be used within the communications system illustrated inFIG. 1A;

FIG. 1C is a system diagram of an example radio access network and anexample core network that may be used within the communications systemillustrated in FIG. 1A;

FIG. 2A is diagram of an example membership status array field;

FIG. 2B is a diagram of an example user position array field;

FIG. 3A is a diagram of an example downlink multi-user channel accessscheme;

FIG. 3B is a diagram of an example uplink (UL) multi-user channel accessscheme;

FIG. 4 is a diagram of an example procedure for updating a positionbit-field per transmission;

FIG. 5 is a diagram of an example of an alternative procedure forupdating a position bit-field per transmission;

FIG. 6 is a diagram of an example null data packet (NDP) MAC frame body;

FIG. 7 is a diagram of an example multi-user (MU) clustering mechanismin which MU clustering is signaled on an MU data transmission;

FIG. 8 is a diagram of an example alternative method of MU clusteringwhere the MU clustering scheduling is transmitted in the MU controlframe immediately preceding the MU data transmission;

FIG. 9 is a diagram of an example high efficiency (HE) NDP MAC physicallayer convergence protocol (PLCP) protocol data unit (PPDU) according toa first example HE NDP MAC PPDU;

FIG. 10 is a diagram of an example HE NDP MAC PPDU according to a secondexample HE NDP MAC PPDU embodiment;

FIG. 11 is a diagram of a first example embodiment of an HE NDPmulti-user-request-to-send (MU-RTS) frame;

FIG. 12 is a flow diagram of example high-efficiency multi-user (HE MU)procedures using the example NDP MU control frame of FIG. 11 ;

FIG. 13 is a diagram of a second example embodiment of an HE NDP MU-RTSframe;

FIG. 14 is a flow diagram of example HE MU procedures using the exampleNDP MU control frame of FIG. 13 ;

FIG. 15 is a diagram of a third example embodiment of an HE NDP MU-RTSframe;

FIG. 16 is a flow diagram of example HE MU procedures using the exampleNDP MU control frame of FIG. 15 ;

FIG. 17 is a diagram of an example embodiment of an HE NDPmulti-user-clear-to-send (MU-CTS) frame body;

FIG. 18 is a flow diagram of example HE MU procedures using the exampleNDP MU control frame of FIG. 17 ;

FIG. 19 is a diagram of a first example NDP MU-Poll frame bodyembodiment;

FIG. 20 is a flow diagram of example HE MU procedures using the exampleNDP MU control frame of FIG. 19 ;

FIG. 21 is a diagram of a second example NDP MU-Poll frame bodyembodiment;

FIG. 22 is a flow diagram of example HE MU procedures using the exampleNDP MU control frame of FIG. 21 ;

FIG. 23 is a diagram of a third example NDP MU-Poll frame bodyembodiment;

FIG. 24 is a flow diagram of example HE MU procedures using the exampleNDP MU control frame of FIG. 23 ;

FIG. 25 is a diagram of a fourth example NDP MU-Poll frame bodyembodiment;

FIG. 26 is a flow diagram of example HE MU procedures using the exampleNDP MU control frame of FIG. 25 ;

FIG. 27 is a flow diagram of example HE MU procedures using a NDP MUschedule control frame;

FIG. 28 is a diagram of an example HE NDP uplink response/request (ULR)frame body;

FIG. 29 is a flow diagram of example HE MU procedures using the exampleNDP MU control frame of FIG. 28 ;

FIG. 30 is a graph showing the result of an analysis comparing baselineand uplink (UL) orthogonal frequency division multiple access (OFDMA)transmission for full MAC control frames and UL OFDMA transmission withthe example NDP MAC frames described herein for large packets;

FIG. 31 is a graph showing the result of analysis comparing baseline andUL OFDMA transmission for full MAC control frames and UL OFDMAtransmission with the example NDP MAC frames described herein for smallpackets;

FIG. 32 is a diagram of an example abstracted model for single user (SU)transmissions and UL MU transmissions;

FIG. 33 is a graph representing example design requirements fordifferent targeted gains for UL MU transmissions involving 4 OFDMAusers;

FIG. 34 is a graph representing example design requirements fordifferent targeted gains for UL MU transmissions involving 8 OFDMAusers;

FIG. 35 is a graph representing a design requirement for UL MU controlframes with 4 OFDMA users when data symbol length is fixed; and

FIG. 36 is a graph representing a design requirement for UL MU controlframes with 8 OFDMA users when data symbol length is fixed.

DETAILED DESCRIPTION

FIG. 1A is a diagram of an example communications system 100 in whichone or more disclosed embodiments may be implemented. The communicationssystem 100 may be a multiple access system that provides content, suchas voice, data, video, messaging, broadcast, etc., to multiple wirelessusers. The communications system 100 may enable multiple wireless usersto access such content through the sharing of system resources,including wireless bandwidth. For example, the communications systems100 may employ one or more channel access methods, such as code divisionmultiple access (CDMA), time division multiple access (TDMA), frequencydivision multiple access (FDMA), orthogonal FDMA (OFDMA), single-carrierFDMA (SC-FDMA), and the like.

As shown in FIG. 1A, the communications system 100 may include wirelesstransmit/receive units (WTRUs) 102 a, 102 b, 102 c, 102 d, a radioaccess network (RAN) 104, a core network 106, a public switchedtelephone network (PSTN) 108, the Internet 110, and other networks 112,though it will be appreciated that the disclosed embodiments contemplateany number of WTRUs, base stations, networks, and/or network elements.Each of the WTRUs 102 a, 102 b, 102 c, 102 d may be any type of deviceconfigured to operate and/or communicate in a wireless environment. Byway of example, the WTRUs 102 a, 102 b, 102 c, 102 d may be configuredto transmit and/or receive wireless signals and may include userequipment (UE), a mobile station (STA), a fixed or mobile subscriberunit, a pager, a cellular telephone, a personal digital assistant (PDA),a smartphone, a laptop, a netbook, a personal computer, a wirelesssensor, consumer electronics, and the like. WTRU, UE, STA and the likemay be used interchangeably throughout.

The communications systems 100 may also include a base station 114 a anda base station 114 b. Each of the base stations 114 a, 114 b may be anytype of device configured to wirelessly interface with at least one ofthe WTRUs 102 a, 102 b, 102 c, 102 d to facilitate access to one or morecommunication networks, such as the core network 106, the Internet 110,and/or the other networks 112. By way of example, the base stations 114a, 114 b may be a base transceiver station (BTS), a Node-B, an eNode B,a Home Node B, a Home eNode B, a site controller, an access point (AP),a wireless router, and the like. While the base stations 114 a, 114 bare each depicted as a single element, it will be appreciated that thebase stations 114 a, 114 b may include any number of interconnected basestations and/or network elements.

The base station 114 a may be part of the RAN 104, which may alsoinclude other base stations and/or network elements (not shown), such asa base station controller (BSC), a radio network controller (RNC), relaynodes, etc. The base station 114 a and/or the base station 114 b may beconfigured to transmit and/or receive wireless signals within aparticular geographic region, which may be referred to as a cell (notshown). The cell may further be divided into cell sectors. For example,the cell associated with the base station 114 a may be divided intothree sectors. Thus, in one embodiment, the base station 114 a mayinclude three transceivers, i.e., one for each sector of the cell. Inanother embodiment, the base station 114 a may employ multiple-inputmultiple-output (MIMO) technology and, therefore, may utilize multipletransceivers for each sector of the cell.

The base stations 114 a, 114 b may communicate with one or more of theWTRUs 102 a, 102 b, 102 c, 102 d over an air interface 116, which may beany suitable wireless communication link (e.g., radio frequency (RF),microwave, infrared (IR), ultraviolet (UV), visible light, etc.). Theair interface 116 may be established using any suitable radio accesstechnology (RAT).

More specifically, as noted above, the communications system 100 may bea multiple access system and may employ one or more channel accessschemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, and the like. Forexample, the base station 114 a in the RAN 104 and the WTRUs 102 a, 102b, 102 c may implement a radio technology such as Universal MobileTelecommunications System (UMTS) Terrestrial Radio Access (UTRA), whichmay establish the air interface 116 using wideband CDMA (WCDMA). WCDMAmay include communication protocols such as High-Speed Packet Access(HSPA) and/or Evolved HSPA (HSPA+). HSPA may include High-Speed DownlinkPacket Access (HSDPA) and/or High-Speed Uplink Packet Access (HSUPA).

In another embodiment, the base station 114 a and the WTRUs 102 a, 102b, 102 c may implement a radio technology such as Evolved UMTSTerrestrial Radio Access (E-UTRA), which may establish the air interface116 using Long Term Evolution (LTE) and/or LTE-Advanced (LTE-A).

In other embodiments, the base station 114 a and the WTRUs 102 a, 102 b,102 c may implement radio technologies such as IEEE 802.16 (i.e.,Worldwide Interoperability for Microwave Access (WiMAX)), CDMA2000,CDMA2000 1×, CDMA2000 EV-DO, Interim Standard 2000 (IS-2000), InterimStandard 95 (IS-95), Interim Standard 856 (IS-856), Global System forMobile communications (GSM), Enhanced Data rates for GSM Evolution(EDGE), GSM EDGE (GERAN), and the like.

The base station 114 b in FIG. 1A may be a wireless router, Home Node B,Home eNode B, or access point, for example, and may utilize any suitableRAT for facilitating wireless connectivity in a localized area, such asa place of business, a home, a vehicle, a campus, and the like. In oneembodiment, the base station 114 b and the WTRUs 102 c, 102 d mayimplement a radio technology such as IEEE 802.11 to establish a wirelesslocal area network (WLAN). In another embodiment, the base station 114 band the WTRUs 102 c, 102 d may implement a radio technology such as IEEE802.15 to establish a wireless personal area network (WPAN). In yetanother embodiment, the base station 114 b and the WTRUs 102 c, 102 dmay utilize a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE,LTE-A, etc.) to establish a picocell or femtocell. As shown in FIG. 1A,the base station 114 b may have a direct connection to the Internet 110.Thus, the base station 114 b may not be required to access the Internet110 via the core network 106.

The RAN 104 may be in communication with the core network 106, which maybe any type of network configured to provide voice, data, applications,and/or voice over internet protocol (VoIP) services to one or more ofthe WTRUs 102 a, 102 b, 102 c, 102 d. For example, the core network 106may provide call control, billing services, mobile location-basedservices, pre-paid calling, Internet connectivity, video distribution,etc., and/or perform high-level security functions, such as userauthentication. Although not shown in FIG. 1A, it will be appreciatedthat the RAN 104 and/or the core network 106 may be in direct orindirect communication with other RANs that employ the same RAT as theRAN 104 or a different RAT. For example, in addition to being connectedto the RAN 104, which may be utilizing an E-UTRA radio technology, thecore network 106 may also be in communication with another RAN (notshown) employing a GSM radio technology.

The core network 106 may also serve as a gateway for the WTRUs 102 a,102 b, 102 c, 102 d to access the PSTN 108, the Internet 110, and/orother networks 112. The PSTN 108 may include circuit-switched telephonenetworks that provide plain old telephone service (POTS). The Internet110 may include a global system of interconnected computer networks anddevices that use common communication protocols, such as thetransmission control protocol (TCP), user datagram protocol (UDP) andthe internet protocol (IP) in the TCP/IP internet protocol suite. Thenetworks 112 may include wired or wireless communications networks ownedand/or operated by other service providers. For example, the networks112 may include another core network connected to one or more RANs,which may employ the same RAT as the RAN 104 or a different RAT.

Some or all of the WTRUs 102 a, 102 b, 102 c, 102 d in thecommunications system 100 may include multi-mode capabilities, i.e., theWTRUs 102 a, 102 b, 102 c, 102 d may include multiple transceivers forcommunicating with different wireless networks over different wirelesslinks. For example, the WTRU 102 c shown in FIG. 1A may be configured tocommunicate with the base station 114 a, which may employ acellular-based radio technology, and with the base station 114 b, whichmay employ an IEEE 802 radio technology.

FIG. 1B is a system diagram of an example WTRU 102. As shown in FIG. 1B,the WTRU 102 may include a processor 118, a transceiver 120, atransmit/receive element 122, a speaker/microphone 124, a keypad 126, adisplay/touchpad 128, non-removable memory 130, removable memory 132, apower source 134, a global positioning system (GPS) chipset 136, andother peripherals 138. It will be appreciated that the WTRU 102 mayinclude any sub-combination of the foregoing elements while remainingconsistent with an embodiment.

The processor 118 may be a general purpose processor, a special purposeprocessor, a conventional processor, a digital signal processor (DSP), aplurality of microprocessors, one or more microprocessors in associationwith a DSP core, a controller, a microcontroller, Application SpecificIntegrated Circuits (ASICs), Field Programmable Gate Array (FPGAs)circuits, any other type of integrated circuit (IC), a state machine,and the like. The processor 118 may perform signal coding, dataprocessing, power control, input/output processing, and/or any otherfunctionality that enables the WTRU 102 to operate in a wirelessenvironment. The processor 118 may be coupled to the transceiver 120,which may be coupled to the transmit/receive element 122. While FIG. 1Bdepicts the processor 118 and the transceiver 120 as separatecomponents, it will be appreciated that the processor 118 and thetransceiver 120 may be integrated together in an electronic package orchip.

The transmit/receive element 122 may be configured to transmit signalsto, or receive signals from, a base station (e.g., the base station 114a) over the air interface 116. For example, in one embodiment, thetransmit/receive element 122 may be an antenna configured to transmitand/or receive RF signals. In another embodiment, the transmit/receiveelement 122 may be an emitter/detector configured to transmit and/orreceive IR, UV, or visible light signals, for example. In yet anotherembodiment, the transmit/receive element 122 may be configured totransmit and receive both RF and light signals. It will be appreciatedthat the transmit/receive element 122 may be configured to transmitand/or receive any combination of wireless signals.

In addition, although the transmit/receive element 122 is depicted inFIG. 1B as a single element, the WTRU 102 may include any number oftransmit/receive elements 122. More specifically, the WTRU 102 mayemploy MIMO technology. Thus, in one embodiment, the WTRU 102 mayinclude two or more transmit/receive elements 122 (e.g., multipleantennas) for transmitting and receiving wireless signals over the airinterface 116.

The transceiver 120 may be configured to modulate the signals that areto be transmitted by the transmit/receive element 122 and to demodulatethe signals that are received by the transmit/receive element 122. Asnoted above, the WTRU 102 may have multi-mode capabilities. Thus, thetransceiver 120 may include multiple transceivers for enabling the WTRU102 to communicate via multiple RATs, such as UTRA and IEEE 802.11, forexample.

The processor 118 of the WTRU 102 may be coupled to, and may receiveuser input data from, the speaker/microphone 124, the keypad 126, and/orthe display/touchpad 128 (e.g., a liquid crystal display (LCD) displayunit or organic light-emitting diode (OLED) display unit). The processor118 may also output user data to the speaker/microphone 124, the keypad126, and/or the display/touchpad 128. In addition, the processor 118 mayaccess information from, and store data in, any type of suitable memory,such as the non-removable memory 130 and/or the removable memory 132.The non-removable memory 130 may include random-access memory (RAM),read-only memory (ROM), a hard disk, or any other type of memory storagedevice. The removable memory 132 may include a subscriber identitymodule (SIM) card, a memory stick, a secure digital (SD) memory card,and the like. In other embodiments, the processor 118 may accessinformation from, and store data in, memory that is not physicallylocated on the WTRU 102, such as on a server or a home computer (notshown).

The processor 118 may receive power from the power source 134, and maybe configured to distribute and/or control the power to the othercomponents in the WTRU 102. The power source 134 may be any suitabledevice for powering the WTRU 102. For example, the power source 134 mayinclude one or more dry cell batteries (e.g., nickel-cadmium (NiCd),nickel-zinc (NiZn), nickel metal hydride (NiMH), lithium-ion (Li-ion),etc.), solar cells, fuel cells, and the like.

The processor 118 may also be coupled to the GPS chipset 136, which maybe configured to provide location information (e.g., longitude andlatitude) regarding the current location of the WTRU 102. In additionto, or in lieu of, the information from the GPS chipset 136, the WTRU102 may receive location information over the air interface 116 from abase station (e.g., base stations 114 a, 114 b) and/or determine itslocation based on the timing of the signals being received from two ormore nearby base stations. It will be appreciated that the WTRU 102 mayacquire location information by way of any suitablelocation-determination method while remaining consistent with anembodiment.

The processor 118 may further be coupled to other peripherals 138, whichmay include one or more software and/or hardware modules that provideadditional features, functionality and/or wired or wirelessconnectivity. For example, the peripherals 138 may include anaccelerometer, an e-compass, a satellite transceiver, a digital camera(for photographs or video), a universal serial bus (USB) port, avibration device, a television transceiver, a hands free headset, aBluetooth® module, a frequency modulated (FM) radio unit, a digitalmusic player, a media player, a video game player module, an Internetbrowser, and the like.

FIG. 1C is a system diagram of the RAN 104 and the core network 106according to an embodiment. As noted above, the RAN 104 may employ anE-UTRA radio technology to communicate with the WTRUs 102 a, 102 b, 102c over the air interface 116. The RAN 104 may also be in communicationwith the core network 106.

The RAN 104 may include eNode-Bs 140 a, 140 b, 140 c, though it will beappreciated that the RAN 104 may include any number of eNode-Bs whileremaining consistent with an embodiment. The eNode-Bs 140 a, 140 b, 140c may each include one or more transceivers for communicating with theWTRUs 102 a, 102 b, 102 c over the air interface 116. In one embodiment,the eNode-Bs 140 a, 140 b, 140 c may implement MIMO technology. Thus,the eNode-B 140 a, for example, may use multiple antennas to transmitwireless signals to, and receive wireless signals from, the WTRU 102 a.

Each of the eNode-Bs 140 a, 140 b, 140 c may be associated with aparticular cell (not shown) and may be configured to handle radioresource management decisions, handover decisions, scheduling of usersin the uplink and/or downlink, and the like. As shown in FIG. 1C, theeNode-Bs 140 a, 140 b, 140 c may communicate with one another over an X2interface.

The core network 106 shown in FIG. 1C may include a mobility managementgateway (MME) 142, a serving gateway 144, and a packet data network(PDN) gateway 146. While each of the foregoing elements are depicted aspart of the core network 106, it will be appreciated that any one ofthese elements may be owned and/or operated by an entity other than thecore network operator.

The MME 142 may be connected to each of the eNode-Bs 142 a, 142 b, 142 cin the RAN 104 via an S1 interface and may serve as a control node. Forexample, the MME 142 may be responsible for authenticating users of theWTRUs 102 a, 102 b, 102 c, bearer activation/deactivation, selecting aparticular serving gateway during an initial attach of the WTRUs 102 a,102 b, 102 c, and the like. The MME 142 may also provide a control planefunction for switching between the RAN 104 and other RANs (not shown)that employ other radio technologies, such as GSM or WCDMA.

The serving gateway 144 may be connected to each of the eNode Bs 140 a,140 b, 140 c in the RAN 104 via the S1 interface. The serving gateway144 may generally route and forward user data packets to/from the WTRUs102 a, 102 b, 102 c. The serving gateway 144 may also perform otherfunctions, such as anchoring user planes during inter-eNode B handovers,triggering paging when downlink data is available for the WTRUs 102 a,102 b, 102 c, managing and storing contexts of the WTRUs 102 a, 102 b,102 c, and the like.

The serving gateway 144 may also be connected to the PDN gateway 146,which may provide the WTRUs 102 a, 102 b, 102 c with access topacket-switched networks, such as the Internet 110, to facilitatecommunications between the WTRUs 102 a, 102 b, 102 c and IP-enableddevices. An access router (AR) 150 of a wireless local area network(WLAN) 155 may be in communication with the Internet 110. The AR 150 mayfacilitate communications between APs 160 a, 160 b, and 160 c. The APs160 a, 160 b, and 160 c may be in communication with STAs 170 a, 170 b,and 170 c.

The core network 106 may facilitate communications with other networks.For example, the core network 106 may provide the WTRUs 102 a, 102 b,102 c with access to circuit-switched networks, such as the PSTN 108, tofacilitate communications between the WTRUs 102 a, 102 b, 102 c andtraditional land-line communications devices. For example, the corenetwork 106 may include, or may communicate with, an IP gateway (e.g.,an IP multimedia subsystem (IMS) server) that serves as an interfacebetween the core network 106 and the PSTN 108. In addition, the corenetwork 106 may provide the WTRUs 102 a, 102 b, 102 c with access to thenetworks 112, which may include other wired or wireless networks thatare owned and/or operated by other service providers.

IEEE 802.11ac introduced a group ID concept, which is mainly used fordownlink (DL) multi-user multiple-input/multiple-output (MIMO) (MU-MIMO)transmissions to enable the AP to address a group of STAs with a singlegroup ID. The single group ID may be included in a VHT signal A(VHT-SIG-A) field of a physical layer frame. A Signal field is used todescribe the data payload of the physical layer frame. The purpose ofthe Signal field is to help the receiver decode the data payload, whichis done by describing the parameters used for transmission. 802.11acseparates the signal into two different parts, called the Signal A andSignal B fields (i.e., SIG-A and SIG-B fields). The former is in thepart of the physical layer header that is received identically by allreceivers; the latter is in the part of the physical layer header thatis different for each multi-user receiver. In the IEEE 802.11acstandard, the AP may use group ID management frames to assign a group IDto STAs. Group ID management frames may be addressed to the individualSTAs and may include a membership status array and a user positionarray. FIG. 2A is a diagram of an example membership status array field,which may indicate the receiving STA's membership in one or more groups.FIG. 2B is a diagram of an example user position array field, which mayindicate the receiving STA's position within each of the groups that itis a member of.

An IEEE 802.11ah task group has been established to develop support forWiFi systems in the sub 1 GHz band. The IEEE 802.11ah physical layer(PHY) is required to support 1, 2, 4, 8, and 16 MHz bandwidths. Nulldata packets (NDPs) have been introduced in the IEEE 802.11ah standardto carry simple control and management information, including definitionof NDP Clear-To-Send (CTS) frames, NDP Contention-Free End (CF-End)frames, NDP Power-Save Poll (PS Poll) frames, NDP Acknowledgement (ACK)frames, NDP Block Acknowledgement (BA) frames, NDP Beamforming ReportPoll frames, NDP Paging frames, and NDP Probe Request frames.Coordinated orthogonal block-based resource allocation (COBRA), MUparallel channel access (MU-PCA), uplink (UL) MU-MIMO, and preambledesigns have previously addressed alternative aspects of simultaneousmulti-user transmissions.

FIG. 3A is a diagram of an example downlink (DL) multi-user channelaccess scheme. The example multi-user channel access scheme illustratedin FIG. 3A includes two control frames, group-request to send (G-RTS)and group-clear to send (G-CTS). A G-RTS frame (also referred to as a DLschedule frame) may be used by an AP to reserve the channel for downlinkMU transmissions as well as for downlink resource allocation. A G-CTSframe may be transmitted by non-AP STAs and may be used to confirm thereception of a G-RTS frame and acknowledge to the AP that the STA isready for a DL MU transmission.

FIG. 3B is a diagram of an example uplink (UL) multi-user channel accessscheme. The example multi-user channel access scheme illustrated in FIG.3B includes a COBRA poll frame, a UL response/request (ULR) frame, aCOBRA schedule frame and an MU ACK frame, with short interframe spaces(SIFSs) therebetween. The COBRA poll frame may be used to poll multipleSTAs for uplink transmissions and may also be referred to, for example,as an MU-Poll frame, a G-Poll frame, or an MU-Request. A ULR frame maybe used by STAs to respond to the Poll frame or to request uplinktransmission and may also be referred to, for example, as an MU-Requestor an MU-Response. A COBRA schedule frame may be used by an AP toschedule uplink transmissions, and may be based on UL channel qualityindication (CQI). An MU ACK frame may be used by an AP to acknowledgethe reception of the previous uplink transmissions.

For multi-user transmission, an AP may need to schedule a group of STAsfor MU communications for a scheduling interval (also referred to hereinas a cluster). For a cluster, it may be desirable to have more dynamicand flexible grouping than is used in the IEEE 802.1 lac groupingprocedures described above to ensure that system spectral efficiency isacceptable.

For example, grouping procedures and associated group ID mechanismsdescribed above with respect to IEEE 802.11ac only support onemulti-user transmission scheme (downlink MU-MIMO), the number ofsupported DL MU-MIMO groups is limited (e.g., up to 62 group IDs), andthe number of simultaneous users is also limited (e.g., up to 4 users).Next generation WLAN systems may need to use multiple MU transmissionschemes in both the DL and UL, which may require support for many moregroups, each of which may need to support more users.

As another example, the MU scheduling scheme described above is notflexible at least because the AP needs to perform separate unicasttransmissions of the group management frame, which includes theinformation regarding user positions within a group. Further, during theMU data transmission, there is no mechanism to modify either themembership or user positions even when channel conditions have beensignificantly changed since the previous group management frametransmission.

Embodiments described herein provide for new MU clustering andscheduling mechanisms, which may support a large number of clusters formultiple MU transmission schemes, a combination of OFDMA clusters andOFDM MU-MIMO groups, and flexible clustering and scheduling mechanismsthat may enable per-transmission scheduling. Further, new MU controlframes are defined herein to enable scheduling of multiple usertransmissions. For example, MU control frames are defined to enable anAP to first poll the STAs and to enable the STAs to reply to the pollframe for uplink MU transmission. Further, because MU control frames areoften considered as extra overhead to MAC efficiency, embodimentsdescribed herein provide schemes to further reduce the overhead of MUcontrol frames to improve control overhead efficiency. For example, MUtransmission may only be desirable when the throughput ratio of MUtransmissions to single user (SU) transmissions is higher than aparticular threshold. Accordingly, embodiments described herein maylimit control overhead, for example, by setting a maximum control frameduration.

Embodiments are described below, which may enable an AP to manage MUclusters and may support a large number of clusters for multiplesimultaneous OFDM-MU-MIMO transmission schemes and flexible clusteringand scheduling mechanisms that may enable per-transmission scheduling.Four specific embodiments of MU clustering and scheduling mechanisms aredescribed as examples, and one of ordinary skill in the art willunderstand that other clustering and scheduling mechanisms are possiblewithin the scope of the described examples.

Further, in order to synchronize between multiple users and acquire thetraffic information for each user, UL MU transmissions may require extracontrol overhead. Traffic information may include, for example, whethera STA has data to send and any requirements for scheduling the MU ULtransmission (e.g., quality of service (QoS), traffic load, traffic ID,or traffic category). For example, MU transmissions may only bedesirable when the throughput ratio of MU transmissions to single user(SU) transmissions is higher than a particular threshold. Accordingly,embodiments are also described below where UL MU control overhead may berequired to satisfy one or more conditions.

In an exemplary embodiment of an MU clustering and scheduling mechanism,an AP may transmit a clustering management frame to a STA or a clusterof STAs that belong to one or more channels. The clustering managementframe may include at least a membership bit-field and a position bitfield.

The membership bit-field may include an array of N bits, where N is thenumber of members in the cluster. The kth bit in the array may be usedto indicate whether the STA belongs to the kth clustering (k=0, . . .N−1). N may be pre-defined or signaled, for example, in a beacon frameor in the clustering management frame. When N is signaled in a beaconframe, N may remain the same for one or more beacon intervals such thatthe number of groups supported by the AP may remain the same for thesebeacon intervals. When N is signaled in the clustering management frame,N may be increased or decreased by the AP using the clusteringmanagement frame.

The position bit-field may include mN bits, where m is the number ofsimultaneous users. Here, each group may have m bits to signal theposition of the users, and m may be pre-defined or signaled, forexample, in the beacon frame or in the clustering management frame. Whenm is signaled in the beacon frame, m may remain the same for one or morebeacon intervals. When m is signaled in the management frame, m may beincreased or decreased by the AP using the clustering management frame.

In an example, the AP may define different clusters based on, forexample, different MU transmission schemes. For example, the AP maydefine clusters for each of downlink OFDM MU-MIMO (per channel)transmission schemes, uplink OFDM MU-MIMO (per channel) transmissionschemes, downlink OFDMA (one or more channels) transmission schemes anduplink OFDMA (one or more channels) transmission schemes. With respectto downlink and uplink OFDM MU-MIMO schemes, OFDM MU-MIMO may or may notbe used in combination with OFDMA clusters, and an OFDM MU-MIMOoperation may be backward compatible to VHT capabilities whether or notit is in combination with OFDMA clusters. With respect to downlink OFDMAclusters, downlink OFDMA may use one or more channels and/or more thanone sub-channel within a channel, wherein clusters may be defined fortransmissions using more than one channel and/or sub-channel. Withrespect to uplink OFDMA clusters, uplink OFDMA may use either more thanone channel or more than one sub-channel within a channel.

In another example, the AP may define one cluster with a relativelylarge N. Here, each MU transmission scheme may be assigned to use acertain range of the cluster IDs, and, in some cases, each MUtransmission scheme may be assigned to use a certain range of thecluster IDs in combination with Group IDs. The number of cluster IDsused by each transmission scheme may be determined in one of a number ofdifferent ways, such as using specifications (“fixed scenario”) or usingsystem signaling (“flexible scenario”).

In the flexible scenario, the AP may include an MU transmission clusterarrangement element in the Beacon frame. The MU transmission clusterarrangement element may define the relationship between an MUtransmission mode and a cluster ID range. For example, for MU mode 0,the relationship may remain unchanged during one or more Beaconintervals. The MU transmission cluster arrangement element may betransmitted in every Beacon frame or periodically in every M Beaconframes. In an alternative example, this element may be transmitted whenthe AP intends to update the cluster ID range assignment. In this way,the cluster ID may imply the MU transmission mode. Thus, in the SIGfield of each transmission, when the cluster ID is present, the MUtransmission mode may not be needed. In another example of the flexiblescenario, the MU cluster range assignment may be included in the clustermanagement frame.

For MU transmissions, the AP may signal the cluster ID in the SIG field.The cluster ID may represent the corresponding group membership (e.g.,membership array) and positions (e.g., position array) within eachgroup. Thus, the cluster of users may acquire the resource blockassigned for them by the cluster ID. The cluster ID may not be unique,especially in a densely deployed system with overlapping base stationsubsystem (OBSS). Therefore, users with a signaled cluster ID may needto check the MAC header to confirm the intended receiver of the packet.

The membership array and position array may be assigned and updatedwithin the clustering management frame. Further, a combination ofMU-MIMO and OFDMA may be possible. In this case, the cluster definitionmay be unique for each of the OFDM MU-MIMO and OFDMA transmissionschemes. Alternatively, a cluster definition may be a combination ofboth for either DL or UL transmissions.

In another exemplary embodiment of an MU clustering and schedulingmechanism, the clustering management frame may have the same format asthat defined for the first embodiment of the MU clustering andscheduling mechanism. However, in this embodiment, the positionbit-field may be updated with each new transmission opportunity (TxOP).

FIG. 4 is a diagram of an example procedure for updating a positionbit-field per transmission. FIG. 4 shows clustering management frames401 and packets 403 transmitted for a MU transmission on thesub-channels. In the example illustrated in FIG. 4 , the membershipbit-field and position bit-field may be signaled in the clusteringmanagement frame and the position bit-field may be updated in the SIGfield, which is included in the physical layer convergence protocol(PLCP) header of the packet. The packet may be a data session/packet,and, more specifically, a PLCP protocol data unit (PPDU), which is acomposite frame comprising a MAC protocol data unit (MPDU) with anadditional PLCP preamble and header appended thereto. In this example,in the clustering management frame, for the kth cluster, sub-channels 1,2, 3, and 4 are assigned to STAs 1, 2, 3, and 4, respectively. In the MUtransmission, which may be either a downlink transmission or an uplinktransmission, cluster k may be signaled in the PLCP header to indicatethe transmission is for STAs 1, 2, 3 and 4. In the PLCP header, theremay be a new subfield, which may indicate the position of the users inthe cluster. The subfield may include a mapping from the positiondefined in the cluster management frame to the position used in theparticular MU transmission. In this example, STA1 used to be in position1 (sub-channel 1) and now is assigned to position 2. STA2 is mapped fromposition 2 to position 4, STA3 remains in the same position, and STA4 ismoved from position 4 to position 1. In general, this mapping may modifynot only the positon of each user, but also the number of resourcesassigned to each user (e.g., multiple sub-channel assignments). Forexample, a user may be assigned to use one sub-channel, while in thereal MU transmission, this user may not be assigned any sub-channel, orit may be assigned to more than one sub-channel.

FIG. 5 is a diagram of an example of an alternative procedure forupdating a position bit-field per transmission. FIG. 5 shows clusteringmanagement frames 501, MU control frames 502 and packets 503 for a MUtransmission on the sub-channels. In the example illustrated in FIG. 5 ,the membership bit-field and position bit-field may be signaled in theclustering management frame. In addition, the position bit-field may beupdated in one or more of the MU control frames, which may betransmitted before the data session/packet. The MU control frame mayinclude a mapping, which may map the position defined in the clustermanagement frame to the position used in the ongoing MU transmission.The mapping may be carried in the SIG field or MAC body of the MUcontrol frame. In an example, the MU control frame may be replaced byany frame transmitted before the MU data transmission, which may includecontrol, scheduling or management information for the MU datatransmission.

In another exemplary embodiment of an MU clustering and schedulingmechanism, the cluster ID may be assigned using an NDP MAC frame. TheNDP PLCP protocol data unit (PPDU) format may follow any of the designsdescribed below.

FIG. 6 is a diagram of an example NDP MAC frame body 600. In the exampleillustrated in FIG. 6 , the NDP Mac Frame Type subfield 601 may be usedto indicate that the frame is an NDP cluster ID assignment frame, the MUmode subfield 602 may be used to indicate the type of MU transmissionmode, the AP address subfield 603 may include a compressed AP address(e.g., partial basic service set identification (BSSID)), the partialassociation ID (PAID) subfield 604 may include a PAID of the STA, andthe assigned cluster ID subfield 605 may be used to indicate theassigned cluster ID. The reserved subfield 606 is not currently used andis reserved for future use.

In another exemplary embodiment of an MU clustering and schedulingmechanism, a cluster ID may not be employed, and a separate clusteringmanagement frame may not be necessary. The clustering membership andposition may be signaled in the MU transmission, either in the controlframe immediately preceding the MU data session or in the PLCPheader/SIG field in the MU data transmission session.

FIG. 7 is a diagram of an example MU clustering mechanism in which MUclustering is signaled on an MU data transmission. In the exampleillustrated in FIG. 7 , a downlink MU transmission may be initiated byan AP, and the AP may not signal any cluster-related information beforethis transmission. The AP may follow the following procedures to assignthe MU cluster. The AP may acquire the media after clear-channelassessment (CCA) and backoff procedures. In the illustrated example, theAP acquires a channel with four sub-channels. The AP may plan to performan MU transmission. In the illustrated example, the AP plans to transmitto four STAs simultaneously using an OFDMA scheme. The AP may prepare,for a MU transmission 700, a PPDU which includes a legacy STF, LTF andSIG field 701, including a legacy short training field (L-STF), a legacylong training field (L-LTF) and a legacy SIG (L-SIG) field, a common SIGfield 702 (e.g., high-efficiency SIG-A (HE-SIG-A) field), ahigh-efficiency (HE) STF and LTF field 703, a dedicated SIG field 704(e.g., high-efficiency SIG-B (HE SIG-B) field), and a data field 705.The legacy fields may enable the system to be backward compatible withother IEEE 802.11 standards, e.g., 802.11a/g, 802.11n, etc.

The common SIG field 702 may be used to carry information to all theusers/STAs in the cluster. The MU transmission mode may be signaled inthe common SIG field, which may be transmitted on all of the acquiredsub-channels and/or with an omni antenna pattern. Thus, it may bedecoded by all the users. In the illustrated example, the HE-SIG-A fieldis the common SIG field, which is modulated and transmitted on eachsub-channel and repeated on the entire channel. Thus, the common SIGfield 702 is the same on each sub-channel. In another example, theHE-SIG-A field may be modulated and transmitted on the entire channel.

The dedicated SIG field 704 may be transmitted to a particular user oneach resource block. The dedicated SIG field 704 may be different oneach sub-channel. The dedicated SIG field 704 may include a STA identityor a compressed version identity, which may indicate that the STA isassigned on that resource block. In the illustrated example, theHE-SIG-B field is the dedicated SIG field. The HE-SIG-B fieldtransmitted on sub-channel 1 (CH1 in FIG. 7 ) may include a PAID orother type of STA identity of STA1. Similarly, the HE-SIG-B fieldtransmitted on sub-channels 2 to 4 may include the PAIDs of STA2, STA3and STA4. In an alternative example, a group ID may be used in theHE-SIG-B field transmitted on a sub-channel. Therefore, a group of STAs,instead of one STA mentioned in the above example, may be assigned fortransmission on the sub-channel. The group of STAs may use some MUtransmission schemes (e.g., MU-MIMO) to communicate with the AP on theassigned sub-channel. The group ID mentioned here may be the MU-MIMOgroup ID defined in IEEE 802.11ac or another type of group ID.

STAs may check the common SIG field 702 and notice that an MUtransmission is followed. In the illustrated example, the STAs decodeall of the dedicated SIG fields 704 (the HE-SIG-B field). If a STA'sidentity is carried in one or more dedicated SIG fields 704, the STA maycontinue the receiving procedure on the corresponding sub-channel(s). Ifthe STA's identity is not presented on one or more of the dedicated SIGfields 704, it may not be the receiver of the MU transmission on thecorresponding sub-channel(s). If the STA's identity is not presented onany of the dedicated SIG fields 704, it may not be the receiver of theMU transmission.

The AP may continue MU data transmission after the preamble. Theresource allocation may follow that signaled in the dedicated SIG field704. On a condition that the STA identity used in the dedicated SIGfield 704 is not unique, the STAs may need to decode the MAC header andconfirm that it is the receiver of the packet.

The MU mechanism described above may work in the case that the MUcluster schedule or arrangement (i.e., the MU clustering management) istransmitted in the same frame as the MU data. In some scenarios, the MUclustering management may be required to be transmitted before the MUdata transmission.

FIG. 8 is a diagram of an alternative method of MU clustering where, fora MU transmission 800, the MU clustering scheduling is transmitted inthe MU control frame 801 immediately preceding the MU data transmission802, with a SIFS disposed therebetween. The MU data transmission 802 maybe either a downlink transmission or an uplink transmission.

In the example illustrated in FIG. 8 , the AP may acquire the mediaafter CCA and backoff procedures. In the illustrated example, the APacquires a channel with four sub-channels. The AP may begin an MUtransmission 800, which may be a downlink MU transmission from the AP tomultiple STAs or an uplink MU transmission from multiple STAs to the AP.The AP may transmit an MU control frame 801 to reserve the transmissionopportunity (TXOP) and perform MU clustering scheduling. The MU controlframe 801 may include a common part 801 a and a dedicated part 801 b.The common part 801 a may reserve the media for a DL MU transmission, ULMU transmission or a combined DL/UL MU transmission. The dedicated part801 b may be different on each sub-channel. The AP may include a PAID orother kind of STA identity in the dedicated part on a certainsub-channel to implicitly indicate that the sub-channel is assigned tothis STA.

In another example, a group ID may be used for a dedicated part 801 btransmitted on a sub-channel. Thus, a group of STAs, instead of one STA,may be assigned for transmission on one sub-channel. The group of STAsmay use some MU transmission schemes (e.g., MU-MIMO) to communicate withthe AP on the assigned sub-channel. The group ID may be the MU-MIMOgroup ID defined in the IEEE 802.11 ac standard or another type of groupID.

The STAs may decode the MU control frame 801. After decoding the commonpart, the STAs may notice the MU TXOP and may compare their PAIDs orother type of STA identities with the ones transmitted in the dedicatedpart 801 a. If the STA's PAID is included in one or more dedicated parts801 a, the STA may be a member of the MU cluster. In one scenario, theSTA may need to decode the MAC header of the MU control packet 801 toconfirm it. The STA may prepare the transmission and/or reception on thecorresponding sub-channels associated with the dedicated part 801 a.Otherwise, the STA may not be part of the MU transmission, and it mayset its NAV accordingly. A short inter-frame space (SIFS) time after theMU control frame 801, the MU data transmission 802 may follow, whichincludes a preamble 802 a and data 802 b. For a DL MU data transmission,the AP may transmit the data frames to multiple users on their assignedsub-channel(s). For a UL MU data transmission, the STAs may begin uplinktransmission on their assigned sub-channel(s).

In an example, the MU control frame 801 may be replaced by any frametransmitted before the MU data transmission 802, which may includecontrol, scheduling or management information for the MU datatransmission 802. In the example illustrated in FIG. 8 , a SIFS is usedbetween the MU control frame 801 and the MU data frame 802. However,other possible inter-frame spacing may be used instead. Further, in theexample illustrated in FIG. 8 , the MU data transmission 802 follows theDL MU control frame 801. However, it may be possible that other controlframes (either DL or UL) may be between the MU data transmission 802 andthe DL MU control frame 801.

As described briefly above, multi-user transmissions may requireadditional control frames, which may be used for resource allocation,synchronization, and the like. These MU control frames may be consideredas overhead to the entire system. Examples described below make use ofnull data packets (NDPs), which may include a PLCP header without theMAC body, to carry MU control messages and/or other MAC information. Theexamples described below include two high efficiency (HE) NDP MAC PPDUdesigns and detailed NDP MU MAC frames.

Examples are described below that make use of an HE NDP MAC PPDU. Two HENDP MAC PPDU examples are described, and one of ordinary skill in theart will appreciate that other HE NDP MAC PPDU designs are possiblewithin the scope of the described examples. In the first HE NDP MAC PPDUexample, only one HE-NDP-SIG field is included in the HE NDP MAC PPDU,while in the second HE NDP MAC PPDU example, the NDP MAC PPDU carriesboth an HE-NDP-SIG-A field and an HE-NDP-SIG-B field.

With respect to the first HE NDP MAC PPDU example, in order to bebackward compatible to other IEEE 802.11 standards, the HE NDP MAC PPDUmay carry a legacy preamble portion.

FIG. 9 is a diagram of an example HE NDP MAC PPDU 900 according to thefirst HE NDP MAC PPDU example. As shown in one example in FIG. 9 ,legacy short training fields (STF), long training fields (LTF) andsignal (SIG) fields may be included in the PPDU as a legacy preambleportion 901. If a system is required to be backward compatible to IEEE802.11a/g, the non-HT-STF (L-STF), non-HT-LTF (L-LTF), and non-HT-SIG(L-SIG) fields may be the same as the legacy portion defined in IEEE802.11n mixed mode. If a system is considered to be backward compatibleto IEEE 802.11n, the L-STF, L-LTF, and L-SIG fields may beunderstandable by IEEE 802.11n and 802.11n+ devices. The legacy part maybe designed in the same way as the HT portion in greenfield mode.

The legacy preamble portion 901 may be transmitted over the conventionalbasic channel bandwidth and duplicated with or without phase rotation onthe entire channel. The basic channel bandwidth may be the smallestbandwidth that is mandatorily supported by the system. For example, whenthe system is operating on the 2.4 GHz band or the 5 GHz band, the basicchannel bandwidth may be 20 MHz. If the AP is operating on an 80 MHzchannel, then the legacy portion 901 may be transmitted on each 20 MHzchannel and repeated on the remaining channels.

In the example illustrated in FIG. 9 , an HE-NDP-SIG field 902 mayfollow the legacy preamble 901 and may use the same number ofsubcarriers as in the L-SIG field. The HE-NDP-SIG field 902 may betransmitted using the same antenna pattern (e.g., omni, sectional orbeamformed antenna pattern) as that used for the L-LTF field.

Some MU transmissions may allow the AP to assign one or moresub-channels to one STA. A sub-channel may be the basic resource unitthat the AP may use for resource allocation. On a condition that thesub-channel size of the MU transmission is the same as the basic channelbandwidth (e.g., the basic channel bandwidth is 20 MHz, the sub-channelbandwidth is also 20 MHz, and the AP is operating on a same or widerchannel), the HE-NDP-SIG field 902 may be transmitted on eachsub-channel and repeated on the entire band. On a condition that thesub-channel size of the MU transmission is less than the basic channelbandwidth (e.g., the basic channel bandwidth is 20 MHz, the sub-channelbandwidth is 5 MHz., and the AP is operating on a same or wider channelbandwidth), the HE-NDP-SIG field 902 may be transmitted on the basicchannel bandwidth. Or in an alternative example, the HE-NDP-SIG field902 may be transmitted on the sub-channel and repeated on the entireband.

The example illustrated in FIG. 9 includes two alternate formats for theHE-NDP-SIG field 902: Format A and Format B.

Format A is an HE-NDP-SIG field 902 with fixed default length (e.g.,fixed in the unit of OFDM symbols). For example, if two OFDM symbols maybe used for the HE-NDP-SIG field 902 and each OFDM symbol contains 48data carriers, then two OFDM symbols may carry 48 information bits givenbinary phase shift keying (BPSK) and a rate 1/2 convolutional code. Theformat A HE-NDP-SIG field 902 illustrated in FIG. 9 includes an NDP MACframe body 903, an NDP indication 904, a cyclic redundancy check (CRC)905 and a tail 906. The NDP MAC frame body subfield 903 may be used tocarry the main information of the control or management frame. The NDPindication subfield 904 may be used to indicate or identify that this isan NDP MAC frame and that this SIG field may not be the same as a normaldata frame and may be re-written. In an alternative example, the NDPindication subfield 904 may be implicitly signaled using the L-STF,L-LTF, or L-SIG fields and may not be explicitly signaled in theHE-NDP-SIG field 902. For example, the length of the L-SIG field may beused to implicitly signal the NDP MAC field. If the length field in theL-SIG field is smaller than a given threshold, the frame may beconsidered as an NDP MAC frame. The tail subfield 906 may be presentedwhen a zero-padding convolutional coding scheme is used for this NDP SIGfield 902. With other coding schemes, or a convolutional coding schemewith a tail-biting technique, the tail subfield 906 may not be required.If, for example, the NDP SIG field 902 carries 48 information bits, theNDP MAC frame body field 903 may include 37 bits (e.g., 1 bit for NDPindication, 4 bits for CRC, and 6 bits for tail).

Format B is an HE-NDP-SIG field 902 with variable length. The Format BHE-NDP-SIG field illustrated in FIG. 9 includes an NDP MAC frame lengthsubfield 907, an NDP MAC frame body 908, an NDP indication subfield 909,a CRC subfield 910 and a tail subfield 911. The NDP MAC frame lengthsubfield 907 may be used to indicate the length of the NDP-SIG field902. This length may be in the unit of OFDM symbols, bits or bytes. TheNDP MAC frame body 908 may be used to carry the main information of thecontrol or management frame. The NDP indication subfield 909 may be usedto indicate that this is an NDP MAC frame and that this SIG field maynot be the same as a normal data frame and may be re-written. Asdescribed above, the NDP indication subfield 909 may be implicitlysignaled using the L-STF, L-LTF, or L-SIG fields and may not beexplicitly signaled in the HE-NDP-SIG field 902. The tail subfield 911may be presented when a zero-padding convolutional coding scheme is usedfor this NDP SIG field 902. With other coding schemes, or aconvolutional coding scheme with a tail-biting technique, the tailsubfield 911 may not be required. If, for example, the NDP SIG field 902carries 48 information bits, the NDP MAC frame body field may contain 37bits (e.g., 1 bit for NDP indication, 4 bits for CRC, and 6 bits fortail). For example, if N OFDM symbols may be used for the NDP MAC frame900, then 24N information bits may be carried. The NDP MAC frame mayinclude 24N−7−x−y bits (e.g., 1 bit for NDP indication, x bits for CRC,y bits for NDP MAC frame length and 6 bits for tail).

FIG. 10 is a diagram of an example HE NDP MAC PPDU 1000 according to thesecond example. With respect to the second HE NDP MAC PPDU example, theexample HE NDP MAC PPDU includes a legacy preamble portion 1001, whichincludes L-STF, L-LTF and L-SIG fields. The transmission rule of thislegacy preamble portion may be the same as that described above withrespect to the first example. Followed by the legacy preamble portion,two NDP SIG fields 1002 and 1003 may be present.

The HE-NDP-SIG-A field 1002 may include common information to all of theusers. This field may be transmitted over the basic channel bandwidthand repeated over the entire band. In one example, the AP may operate ona 20 MHz channel while the basic channel bandwidth may also be 20 MHz.The sub-channel size may be less than 20 MHz (e.g., 5 MHz). Then, theHE-NDP-SIG-A field 1002 may be transmitted over the 20 MHz channel. Inanother example, the AP may operate on an 80 MHz channel while the basicchannel bandwidth may also be 20 MHz. The sub-channel size may be 20MHz. Then, the HE-NDP-SIG-A field 1002 may be coded and modulated overthe primary 20 MHz sub-channel and repeated over the remaining threesub-channels.

In the example illustrated in FIG. 10 , the HE-NDP-SIG-A field 1002includes an NDP MAC frame body 1004, an NDP indication subfield 1005, aCRC subfield 1006 and a tail subfield 1007. The NDP MAC frame body maybe used to carry the common information of the control or managementframe. The common information may be broadcast to all of the users. TheNDP indication subfield 1005 may be used to indicate that this is an NDPMAC frame and this SIG field is not the same as a normal data frame andmay be re-written. The NDP indication subfield 1005 may also be used toindicate the particular NDP MAC PPDU format (e.g., whether anHE-NDP-SIG-B field 1003 follows the HE-NDP-SIG-A field 1002 or isincluded in the NDP MAC frame). As described above, the NDP indicationsubfield 1005 may be implicitly signaled using the L-STF, L-LTF, orL-SIG fields and may not be explicitly signaled in the HE-NDP-SIG field1002. The tail subfield 1007 may be presented when a zero-paddingconvolutional coding scheme is used for the NDP SIG field. With othercoding schemes, or a convolutional coding scheme with a tail-bitingtechnique, this field may not be required.

Further, the HE-NDP-SIG B field 1003 may carry a user/resource dedicatedMAC frame body 1008. For a user dedicated HE-NDP-SIG-B field 1003, theHE-NDP-SIG-B field 1003 may be used to carry user-specified-signaling.With an MU-MIMO transmission scheme, the HE-NDP-SIG B field 1003 may bemodulated with the user specified beams. With an OFDMA transmissionscheme, the HE-NDP-SIG B field 1003 may be transmitted on thesub-channel(s) that are allocated to the user. For example, one user maybe allocated two sub-channels, and the HE-NDP-SIG B field 1003 may bemodulated using the two sub-channels. For a resource dedicatedHE-NDP-SIG-B field 1003, the HE-NDP-SIG-B field 1003 may be used tocarry resource-specified-signaling. The resource-specified-signaling maybe required by the user who is allocated to the resource block. With anOFDMA transmission scheme, the HE-NDP-SIG B field 1003 may betransmitted on each sub-channel. If one user is allocated with more thanone sub-channel, the HE-NDP-SIG B field 1003 may be transmitted on onesub-channel and repeated on the remaining assigned sub-channels.

In the example illustrated in FIG. 10 , the HE-NDP-SIG-B field 1003immediately follows the HE-NDP-SIG-A field 1002. In an alternativeexample, an HE-STF field and an HE-LTF field may be inserted between theHE-NDP-SIG-A field 1002 and the HE-NDP-SIG-B field 1003. The HE-STF andHE-LTF fields may be user/resource specific or may be transmitted overthe entire bandwidth.

The HE-NDP-SIG-B field 1003 may use the basic modulation and codingscheme (MCS) (e.g., MCSO). In an alternative example, the HE-NDP-SIG-Bfield 1003 may be modulated by a selected MCS for all of the users. Inthis case, the selected MCS may be signaled in the HE-NDP-SIG-A field1002. In another example, the HE-NDP-SIG-B 1003 field may be modulatedby a user/resource-specific-MCS. Thus, different MCSs may be used fordifferent users/resources. Those MCS values may be signaled in theHE-NDP-SIG-A field 1002.

The HE-NDP-SIG-B field 1003 may include auser/resource-dedicated-MAC-frame-body 1008, a CRC subfield 1009 and atail subfield 1010. The user/resource-dedicated-MAC-frame-body 1008 maybe used to carry the user/resource dedicated information of the controlor management frame. The tail subfield 1010 may be presented when azero-padding convolutional coding scheme is used for the NDP SIG field.With other coding schemes, or a convolutional coding scheme with atail-biting technique, this field may not be required.

Several examples of NDP MAC frame bodies (e.g., to be applied to NDP MACframe bodies 903, 908 and/or 1004) and/or user/resource dedicated MACframe bodies (e.g., to be applied to theuser/resource-dedicated-MAC-frame-body 1008) of HE MU control frames aredescribed below.

For downlink MU transmissions, as illustrated, for example, in FIG. 3A,the involved MU control frames may include the MU-RTS frame and theMU-CTS frame. The MU RTS-frame may be used to reserve the media andschedule the downlink MU transmission. The MU-RTS frame may betransmitted by the AP to multiple STAs and may also be referred to, forexample, as a G-RTS frame or an MU-Schedule frame. The MU-CTS frame maybe transmitted by STAs to respond to the MU-RTS frame. The MU-CTS framemay be used to confirm the reception of an MU-RTS frame and may provideadditional information about the STA to the AP. The MU-CTS frame mayalso be referred to, for example, as a G-RTS frame or a G-ACK frame.

For uplink MU transmissions, as illustrated, for example, in FIG. 3B,the involved MU control frames may include the MU Poll frame, the uplinkresponse/request (ULR) frame, the MU schedule frame and the MU ACKframe. The MU Poll frame may be used by the AP to reserve the media andpoll multiple STAs for uplink transmission. Normally, an AP may transmitthe MU Poll frame to multiple STAs. This MU Poll frame may also bereferred to, for example, as a G-Poll frame or an MU-Request frame. TheULR frame may be used by STAs to respond to the Poll frame or to requesta grant of an uplink transmission (in which case the ULR frame may ormay not be a responding frame to an MU Poll). Normally, the ULR framemay be transmitted from STAs to an AP. If multiple STAs transmit theirULR frames simultaneously, the transmission may be distinguished inspatial, time, frequency or code domains. The ULR frame may also bereferred to, for example, as an MU-Request frame, an MU-Response frame,or an MU-RTS frame. The MU schedule frame may be used by the AP toschedule the uplink transmissions and/or synchronize the uplinktransmission, and may also be referred to as a MU UL schedule frame. TheMU schedule frame may be referred to by other names and may beconsidered as a responding frame to the ULR frame. Normally, an MUschedule frame may be transmitted from an AP to multiple STAs. The MUACK frame may be used by the AP to acknowledge reception of the previousuplink transmissions.

Examples of an HE NDP MU-RTS frame body are described below. An NDPMU-RTS frame may be used by the AP to reserve an MU TXOP and schedule aDL MU transmission. Three examples of an HE NDP MU-RTS frame body aredescribed, and one of ordinary skill in the art will appreciate thatother HE NDP MU-RTS frame designs are possible within the scope of thedescribed examples.

With respect to a first example of an HE NDP MU-RTS frame body, the HENDP MU-RTS frame body may be included in a SIG field of an NDP MAC PPDU,which may use the structure given in the HE NDP MAC PPDU example of FIG.9 described above.

FIG. 11 is a diagram of the first example of an HE NDP MU-RTS frame. Inthe example illustrated in FIG. 11 , the NDP MU-RTS MAC frame body field1100 includes an NDP MAC Frame Type subfield, an MU mode subfield, an APaddress/TA subfield, a Group ID subfield, a duration subfield and areserved subfield.

The NDP MAC Frame Type subfield may be used to indicate that the NDP MACframe is a HE NDP MU-RTS frame such that devices disclosed herein canidentify the frame as a HE NDP MU-RTS frame. The number of bits used forthis subfield may depend on how many NDP MAC frames are defined. When anMU mode subfield is also included, less bits may be needed. Further, theNDP MAC Frame Type subfield may be used to implicitly signal the DL/ULdirection of the frame by defining DL and UL MAC frame types. Or in analternative example, a direction subfield may be explicitly included inthe frame body field 1100.

The MU mode subfield may be used to indicate the MU transmission mode(e.g., MU-MIMO, OFDMA, single user (SU) or time domain multi-useraggregation). In an alternative example, this subfield may be combinedwith the NDP MAC Frame Type subfield.

The AP address/TA subfield may be used to signal the transmitteraddress. When the MU-RTS frame is transmitted by the AP, it may be usedto signal the AP address.

The Group ID subfield may be transmitted from the AP to multiple STAsand may be used to signal the group ID of the STAs.

The Duration subfield may be used to signal the duration of the TXOP.Unintended STAs may use this subfield to set their network allocationvector (NAV).

The Reserved sub-field may be reserved for future use.

The AP may prepare and transmit an HE NDP MU-RTS frame after it acquiresthe media and has traffic for multiple users. FIG. 12 illustrates a flowdiagram of example HE MU procedures using the example NDP MU controlframe of FIG. 11 . In operation 1201, one or more STAs may receive apacket and perform start of packet detection using L-STF and L-LTFfields. By decoding the L-SIG field, the STA may determine the length ofthis transmission. Based on the length of the transmission determinedfrom the L-SIG field, the STA determines whether the length of thetransmission is less than a threshold by a threshold test, comparison orthe like (1202). If the length of the transmission is not less than thethreshold, the STA may determine that the frame is not a NDP frame(1203). On the other hand, if the length of the transmission is lessthan the threshold, the STA may determine that the frame is or may be aNDP frame and may proceed to operation 1204 or 1206 for furtherverification. The STA may continue decoding the HE-NDP-SIG field and maydetermine that this is an NDP MAC frame when the NDP indication field isset to 1 (1204). If the NDP indication field is not set, the STA maydetermine that the frame is not a NDP frame (1205). If the STAdetermines that the NDP indication field is set, the STA my determinethat the frame is or may be a NDP frame and may proceed to operation1206 for further processing of the NDP MU control frame. It will beappreciated that only one of operations 1202 and 1204 may be providedfor determining whether the frame is a NDP frame.

The STA may revisit the NDP MAC frame body subfield (1206) (e.g., theNDP MAC Frame body subfield 1100). Here, the STA checks the NDP MACframe type and MU mode fields which may identify or indicate the MU-RTSframe and the MU transmission mode (1207) such that the STA candetermine the same. In addition, the STA may check the AP address, GroupID, and/or Cluster ID field (not shown), and may determine whether theSTA is an intended receiver of the MU transmission (1208). If the STA isassociated with the AP, and the group ID is the same as that transmittedin the frame, the STA may be considered to be one of the intendedreceivers and proceed to operation 1209.

For example, an AP may be associated with many STAs (e.g., 100 STAs).The AP may include its signature (e.g., its AP address) in the SIGfield. All of the 100 associated STAs may notice that a transmission isfrom their associated AP based on analyzing the AP address. Based onanalyzing the AP addresses and confirming that the STA is an associatedSTA, the associated STAs may continue read the packet. Unassociated STAsmay by drop the packet and defer for a duration. The AP may furtherdecide to perform a MU transmission to a group or subset of STAs whichare associated with it (e.g., 8 STAs). The information that a STA is anintended receiver may be included in the group ID and/or cluster ID. The8 STAs here are may be referred to as intended recipient/receiver orintended STAs. Therefore, in order to determine whether a STA is anintended STA, the STA may check the AP address, if not previouslyperformed, and check at least one of the group ID and cluster IDprovided in the SIG field.

In operation 1209 the STA may begin preparing a responding frame, e.g.,an MU-CTS frame transmission, to be transmitted after a SIFS timefollowing the end of the MU-RTS transmission. Otherwise, the STA maydetermine it is not part of the transmission, and it may check theduration field and set up NAV accordingly (1210).

With respect to a second example of a HE NDP MU-RTS frame body, the HENDP MU-RTS frame body may be included in a SIG field of an NDP MAC PPDU,which may use the structure given in the first example HE NDP MAC PPDUshown in FIG. 9 .

FIG. 13 is a diagram of a second example of an HE NDP MU-RTS frame 1300.In the example illustrated in FIG. 13 , most of the subfields aresimilar to the first example shown in FIG. 11 . However, the subfieldsmay use a different number of bits and may include an additionalsubfield, the response protocol subfield. The response protocol subfieldmay be used to indicate one or more of the following: a format of theresponse frame (e.g., whether the replying frame is an NDP frame or anormal frame with a MAC body), whethersub-channel-selection-related-information is required in the responseframe, whether synchronization information is required in the responseframe and whether the multiple desired receivers transmit the responseframes simultaneously in the frequency, time, and code domains.

Sub-channel-selection-related-information may include, for example, therank or order of the sub-channels, the measurement (such as thesignal-to-interference-plus-noise ratio (SINR) or a received signalstrength indicator (RSSI) on each sub-channel) or the best and/or worstsub-channel(s). Synchronization information may include, for example,the transmit power, link margin, timestamp compressed timestamp, orcarrier frequency offset. Simultaneous transmission in the frequencydomain may mean that the STAs transmit response frames on their assignedsub-channels, which may not overlap with each other. Simultaneoustransmission in the time domain may mean that the STAs transmit responseframes on different time slots. The AP may or may not poll them beforeeach uplink transmission. Simultaneous transmission in the code domainmay mean that the STAs use the same time-frequency resource to transmitthe response frames. However, they may use pre-defined orthogonalsequences such that the AP may distinguish them at the receiver.

FIG. 14 illustrates a flow diagram of example HE MU procedures using theexample NDP MU control frame of FIG. 13 . Operations 1401-1410 aresimilar to operations 1201-1210 in FIG. 12 , respectively, except inoperation 1409 the STA may additionally check the response protocolfield for preparing a responding frame, e.g., an MU-CTS frametransmission. For example, in operation 1401, One or more STAs mayreceive a packet and perform start of packet detection using L-STF andL-LTF fields. By decoding the L-SIG field, the STA may determine thelength of this transmission. Based on the length of the transmissiondetermined from the L-SIG field, the STA determines whether the lengthof the transmission is less than a threshold by a threshold test,comparison or the like (1402). If the length of the transmission is notless than the threshold, the STA may determine that the frame is not aNDP frame (1403). On the other hand, if the length of the transmissionis less than the threshold, the STA may determine that the frame is ormay be a NDP frame and may proceed to operation 1404 or 1406 for furtherverification. The STA may continue decoding the HE-NDP-SIG field and maydetermine that this is an NDP MAC frame when the NDP indication field isset to 1 (1404). If the NDP indication field is not set, the STA maydetermine that the frame is not a NDP frame (1405). If the STAdetermines that the NDP indication field is set, the STA my determinethat the frame is or may be a NDP frame and may proceed to operation1406 for further processing of the NDP MU control frame. It will beappreciated that only one of operations 1402 and 1404 may be providedfor determining whether the frame is a NDP MAC frame according to theconditions (i.e., NDP condition) therein.

The STA may revisit the NDP MAC frame body subfield (1406) (e.g., theNDP MAC Frame body subfield 1300). Here, the STA checks the NDP MACframe type and MU mode fields which may identify or indicate the MU-RTSframe and the MU transmission mode (1407) such that the STA candetermine the same. In addition, the STA may check the AP address, GroupID, and/or Cluster ID field (not shown), and may determine whether theSTA is an intended receiver of the MU transmission (1408). If the STA isassociated with the AP, and the group ID is the same as that transmittedin the frame, the STA may be considered to be one of the intendedreceivers and proceed to operation 1409. In operation 1409 the STA maycheck the Response Protocol field and may prepare sub-channel selectionand synchronization information accordingly. In operation 1409 the STAmay begin preparing a responding frame, e.g., an MU-CTS frametransmission, to be transmitted after a SIFS time following the end ofthe MU-RTS transmission. The transmission scheme of the MU-CTS frame(e.g., whether the multiple users transmit the MU-CTS framesimultaneously or sequentially, whether it is an NDP frame or a full MACframe, etc.) may follow the indication of the Response Protocol field aswell. Otherwise, the STA may determine it is not part of thetransmission, and it may check the duration field and set up NAVaccordingly (1410).

With respect to a third example of an HE NDP MU-RTS frame body, this NDPframe body shown in FIG. 15 may be included in a SIG field of an NDP MACPPDU, which may use the structure given in the second HE NDP MAC PPDUexample as shown in FIG. 10 , where NDP-SIG-A and NDP-SIG-B fields maybe used.

FIG. 15 is a diagram of the third example of an HE NDP MU-RTS frame1500. In the example illustrated in FIG. 15 , the NDP frame body 1500 acontained in the NDP-SIG-A field (e.g., NDP-SIG-A field 1002) mayinclude an NDP Mac Frame Type subfield, an MU mode subfield, an APaddress/TA subfield, a duration subfield, a synchronization infosubfield, a bandwidth (BW) subfield, an NDP-SIG-B present subfield and areserved subfield.

The NDP MAC Frame Type subfield may be used to indicate or identify theframe as a HE NDP MU-RTS frame to the STA. The MU mode subfield may beused to indicate or identify the MU transmission mode (e.g., MU-MIMO,OFDMA, SU or time domain multi-user aggregation) to the STA. In analternative example, this mode may be combined with the NDP MAC FrameType subfield. The AP address/TA subfield may be used to signal orprovide the transmitter address. When the MU-RTS frame is transmitted bythe AP, the AP address/TA subfield may be used to signal or provide theAP address to the STA. The Duration subfield may be used to signal orprovide the duration of the TXOP to the STA. Unintended STAs may usethis subfield to set NAV.

The Synchronization Info subfield may includetime/frequency/power-synchronization-related-information transmittedfrom the AP to the STAs, or the AP may use this subfield to require theSTAs to respond with requiredtime/frequency/power-synchronization-related-information. This subfieldmay be included in the NDP-SIG-A field (as illustrated in FIG. 15 ), andthe synchronization info may be shared with all the STAs/users. In analternative example, this subfield may be included in the NDP-SIG-Bfield (e.g., NDP-SIG-B field 1003), and the subfield may include userspecific/STA-dedicated-synchronization-information. The BW subfield maybe used to indicate bandwidth, which may be one or more of an operationbandwidth of the AP, an acquired bandwidth in the TXOP, or thesub-channel bandwidth (e.g., where the basic sub-channel size may bevaried per transmission). As an example of the bandwidth being acquiredin the TXOP, an AP that operates on 80 MHz may only acquire 60 MHzsub-channels, so the acquired bandwidth may be 60 MHz. The NDP-SIG-Bpresent subfield may be used to signal whether the NDP-SIG-B field(e.g., NDP-SIG-B field 1003) follows the NDP-SIG-A field (e.g.,NDP-SIG-A field 1002) such the STA is aware to check the NDP-SIG-Bfield. The Reserved subfield may be reserved for future use.

The user/resource dedicated MAC frame body 1500 b contained in theHE-NDP-SIG-B field (e.g., NDP-SIG-B field 1003) may include one or moreof a PAID or a response protocol subfield. The PAID subfield may includea partial AID or other possible ID that may be used to represent theSTA. In an example, the NDP-SIG-B field may be resource/user-dedicated,and, therefore, the PAID subfield may be used to implicitly signal theresource allocation. For example, the NDP-SIG-B field transmitted onsub-channels k and n may carry the same PAID. Then, the user indicatedby the PAID may be allocated to sub-channels k and n. The responseprotocol subfield may be included in the NDP-SIG-B field, and thissubfield may include a user/STA-dedicated response protocol. In analternative example, the response protocol subfield may be included inthe NDP-SIG-A field, and the response protocol may be shared with allthe STAs/users.

The response protocol subfield may be used to indicate and/or identifyone or more of the following: a format of the response frame, whethersub-channel-selection-related-information is included in the responseframe, or whether the multiple desired receivers transmit the responseframes simultaneously in the frequency, time, or code domains. Theformat of the response frame may indicate, for example, whether thereplying frame is an NDP frame or a normal frame with a MAC body. Theresponse protocol subfield may also be used to signal that a DL MUtransmission may follow the frame with xFIS separation. In this way, noresponse frame may be required. With respect to whethersub-channel-selection-related-information is included in the responseframe, sub-channel-selection-related-information may include, forexample, the rank or order of the sub-channels, the measurement (e.g.,signal-to-interference-plus-noise ratio (SINR) or received signalstrength indicator (RSSI) on each sub-channel), or the best and/or worstsub-channel(s).

FIG. 16 illustrates a flow diagram of example HE MU procedures using theexample NDP MU control frame of FIG. 15 . Operations 1601-1605 and 1609are similar to operations 1201-1205 and 1209 in FIG. 12 , respectively.The AP may prepare and transmit the HE NDP MU-RTS frame after itacquires the media and has traffic for multiple users, and STAs mayreceive this packet begin packet detection using L-STF and L-LTF fields.By decoding the L-SIG field, a STA may determine the length of thistransmission and determine whether the frame is a NDP MAC frametherefrom. The STA may continue decoding the HE-NDP-SIG-A field and maydetermine that this is an NDP MAC frame when the NDP indication field isset to 1. The STA may determine that a NDP-SIG-B field may follow whenthe NDP SIG-B Present field is 1 in the NDP-SIG-A field. Afterconfirming that the frame is an NDP frame, the STA may check the NDP MACframe type subfield to determine the type of frame. In operation 1606,the STA may check the AP address in the NDP-SIG-A field and determinewhether it is the associated AP. The STAs that are associated with thisAP may continue checking the NDP-SIG-B field. The STAs that areassociated with this AP may first check in operation 1606 whether theNDP SIG-B Present field is set in the NDP-SIG-A field to determinewhether a NDP-SIG-B field follows the NDP-SIG-A field, if the STA hasn'tperformed this check previously. The STAs that are not associated withthis AP may check the duration field and set their NAV accordingly(1607). The STA may also check the BW field to determine the operatingsub-channels for the MU transmission. These operating sub-channels maybe the sub-channels the AP acquired for transmission and may be the sameas or less than the total operation bandwidth announced by the AP. Inthis way, the OBSS STA may set NAV on the utilized sub-channels and maybe allowed to use the unused sub-channel(s) when they became available.

The STA associated with the AP may continue detecting and processing theNDP-SIG-B field. Since NDP-SIG-B fields transmitted on differentsub-channels may be different, the STA may need to decode all theNDP-SIG-B fields transmitted on all of the sub-channels. By checking thePAID field (or other possible identities) on each sub-channel inoperation 1608, the STA may determine whether it is a STA assigned tothat sub-channel (i.e., the STA determines whether it is an intendedrecipient of the MU-transmission and its resource allocation based on,e.g., the PAID). A STA may be assigned to multiple sub-channels. Thus,the STA may need to decode SIG-B fields on all of the sub-channels.

The STA that are assigned to one or some sub-channels may proceed tooperation 1609 to prepare the responding frames based on the informationcarried in both the NDP-SIG-A and NDP-SIG-B fields. The STA that are notassigned any sub-channel may proceed to operation 1610 and set a NAVaccording to the duration field.

Examples of an HE NDP MU-CTS frame body are described below. An NDPMU-CTS frame may be used by the STA to respond to an MU-RTS frame andconfirm that the STA is ready for DL MU transmission. The HE NDP MU-CTSframe body may be included in a SIG field of an NDP MAC PPDU and may usethe structure given in the HE NDP MAC PPDU shown in FIG. 9 describedabove.

FIG. 17 is a diagram of an example embodiment of an HE NDP MU-CTS framebody 1700. In the example illustrated in FIG. 17 , the NDP MU-CTS MACframe body field 1700 includes an NDP MAC Frame Type subfield, an MUmode subfield, a PAID/TA subfield, a Sub-Channel information subfield, async info field, a Duration subfield and a Reserved subfield.

The NDP MAC Frame Type subfield may be used to indicate and/or identifythe frame as the HE NDP MU-CTS frame. The MU mode subfield may be usedto indicate or identify the MU transmission mode (e.g., MU-MIMO, OFDMA,SU or time domain multi-user aggregation). In an alternative example,the MU mode subfield may be combined with the NDP MAC Frame Typesubfield. The PAID/TA subfield may be used to signal or provide thetransmitter address. When the MU-CTS frame is transmitted by a STA, thePAID/TA subfield may be used to signal or provide the STA address orpartial address.

The Sub-Channel information subfield may be used by the STA to indicatepreferred sub-channel(s). For example, the STA may provide the order orrank of sub-channels according to the received signal strength, or theSTA may provide the received signal measurements, such as SINR or RSSIof each sub-channel. In an alternative example, the STA may provide theindex of the best sub-channel(s) and/or the index of the worstsub-channel(s). Synchronization Info subfield may includetime/frequency/power-synchronization-related-information. The Durationsubfield may be used to signal or provide the duration of the TXOP.Unintended STAs may use the Duration subfield to set their NAV. TheReserved subfield may be reserved for future use.

FIG. 18 illustrates a flow diagram of example HE MU procedures using theexample NDP MU control frame of FIG. 17 . In operation 1801, the STAprepares the NDP MU-CTS MAC frame in response to a NDP MU-RTS MAC frame.During the preparation of the MU-CTS frame, the STA indicates NDP MU-CTSframe in NDP Mac Frame Type field (1802), the STA includes thetransmitter ID in the PAID/TA field (1803), the STA indicates preferredsub-channel in the Sub-Channel Info field (1804) and STA updates theTXOP duration field (1805). The STA may also provide synchronizationinformation in the sync info field (not shown).

The STAs that are the destination of the MU-RTS frame may transmit anMU-CTS frame after a SIFS time following the end of MU-RTS reception.The MU-CTS frame may use the NDP format illustrated in FIG. 17 .

According to the Response Protocol field defined in the MU-RTS frame orpre-defined in the standard, if nothing is shown in the previous MU-RTSframe, the transmission of the NDP MU-CTS may use one or more of thefollowing: time domain division (TDD), frequency domain division (FDD),code domain division, or spatial domain division.

With respect to TDD, the STAs may transmit the NDP MU-CTS framessequentially with or without SIFS separation in between. The order oftransmission may be implicitly signaled by the sub-channel assignment orthe position array in the group ID. In an alternative example, the NDPMU-CTS frame transmitted from a first STA may be transmitted after aSIFS time following the NDP MU-RTS frame. Then, the AP may transmit anNDP frame to poll the next STA. The second STA may transmit the NDPMU-CTS frame when it receives the NDP poll frame. Similar procedures maybe followed for the rest of the transmission of NDP MU-CTS frames fromthe remaining STAs.

With respect to FDD, the STAs may transmit the NDP MU-CTS framessimultaneously but on different frequency sub-channels. The STAs maytransmit the NDP MU-CTS frame on their assigned sub-channel(s). Or theSTAs may transmit on sub-channels by using some mapping function. Themapping function may map a STA to a sub-channel and may be derived bythe sub-channel/resource assignment or position bit field/array definedin the Group ID or cluster ID.

With respect to code domain division, the STA may transmit the NDPMU-CTS frames simultaneously on the same frequency band and may usetheir pre-assigned sequence to modulate the NDP MU-CTS frame. In analternative example, the L-STF, L-LTF, and L-SIG fields from all of theSTA may be the same, and the NDP-SIG field may be modulated by theSTA-specific sequence. With respect to spatial domain division, the STAmay transmit the NDP MU-CTS frames using an uplink MU-MIMO scheme.

The AP may detect all the NDP MU-CTS frames and may re-assignsub-channels to the STAs according to the collected sub-channelinformation field. The AP may prepare the synchronization relatedsignaling according to the synchronization information field and mayprepare the downlink schedule frame (which may also be an NDP frame),which may or may not include the sub-channel assignment andsynchronization information. Or, in an alternative example, the AP mayprepare the downlink MU transmission directly, and, in the PLCP header,the AP may reassign the sub-channel and provide synchronizationinformation. Non-desired STAs may receive this packet and may update orset their NAV accordingly.

Examples of an NDP MU-Poll frame body are described below. An NDPMU-Poll frame may be used by the AP to reserve an MU TXOP and, in anexample, to schedule a UL MU transmission. Four examples of an NDPMU-Poll frame body are described, and one of ordinary skill in the artwill appreciate that other NDP Mu-Poll frame body designs are possiblewithin the scope of the described examples.

With respect to a first example of a NDP MU-Poll frame body, the framebody may be included in a SIG field of an NDP MAC PPDU, which may usethe structure given in the first example embodiment of the HE NDP MACPPDU.

FIG. 19 is a diagram of the first one of the example NDP MU-Poll framebody embodiments. In the example illustrated in FIG. 19 , the NDPMU-Poll MAC frame body field 1900 may include an NDP MAC Frame Typesubfield, an MU mode subfield, an AP address/TA subfield, a GroupID/Multicast PAID subfield, a Duration subfield and a Reserved subfield.

The NDP MAC Frame Type subfield may be used to indicate and/or identifythat this is an HE NDP MU-Poll frame. The MU mode subfield may be usedto indicate and/or identify the MU transmission mode (e.g., MU-MIMO,OFDMA, SU or time domain multi-user aggregation). In an alternativeexample, the MU mode subfield may be combined with the NDP MAC FrameType subfield. The AP address/TA subfield may be used to signal orprovide the transmitter address. When the MU-Poll frame is transmittedby the AP, it may be used to signal or provide the AP address. The GroupID/Multicast PAID subfield may be transmitted from the AP to multipleSTAs and may be used to signal the group ID of the STAs. In analternative example, the Group ID/Multicast PAID subfield may be used tocarry a multicast partial AID, which may include more STAs than typicalMU transmissions. In this case, some polled STAs may not be allocated atime slot in the following UL MU transmissions. The Duration subfieldmay be used to signal the duration of the TXOP. Unintended STAs may usethis subfield to set NAV. The Reserved subfield may be reserved forfuture use.

FIG. 20 illustrates a flow diagram of example HE MU procedures using theexample NDP MU control frame of FIG. 19 . Operations 2001-2010 aresimilar to operations 1201-1210 in FIG. 12 , respectively, with a fewdifferences. For example, in operation 2007, the STA checks the NDP MACframe type field and determines the frame type to be a NDP MU-Pollframe. In addition, in operation 2009, the STA may, after determining itis an intended recipient of the NDP MU-Poll frame in operation 2008,prepare an UL transmission if the STA has traffic in its buffer.

The process shown in FIG. 20 is briefly described. The AP may prepareand transmit the HE NDP MU-Poll frame after it acquires the media andhas traffic for multiple users. STAs may receive this packet and beginpacket detection using the L-STF and L-LTF fields. By decoding the L-SIGfield, a STA may determine the length of this transmission (2001) anddetermine whether the frame is a NDP frame based on a threshold test(2002). STA may continue decoding the HE-NDP-SIG field and may determinethat the received frame is an NDP MAC frame when the NDP indicationfield is set to 1 (2004).

The STA may revisit the NDP Mac Frame body subfield (2006). Here, theNDP Mac Frame Type and MU mode fields may indicate the MU-Poll frame andthe MU transmission mode (2007). By checking the AP address and GroupID/Multicast field, the STA may determine whether it is the intendedrecipient of the MU transmission (2008). If the STA is associated withthe AP, and the group ID is the same as that transmitted in the frame,the STA may be considered as one of the intended receivers. The STA maycheck its uplink traffic buffer and, if data for transmission exists,begin preparing an NDP ULR frame transmission to be transmitted after aSIFS time following the end of the MU-RTS transmission. Otherwise, theSTA may determine it is not part of the transmission, and it may checkthe duration field and set up NAV accordingly.

With respect to a second example of a NDP MU-Poll frame body, the framebody may be included in a SIG field of an NDP MAC PPDU, which may usethe structure given in the HE NDP MAC PPDU shown in FIG. 9 .

FIG. 21 is a diagram of the second example NDP MU-Poll frame body 2100.In the example illustrated in FIG. 21 , most of the subfields aresimilar to the example illustrated in FIG. 19 . However, the subfieldsmay use a different number of bits. One additional subfield, the ULRsubfield, may also be included, which may be used to control a followingULR frame. The ULR protocol subfield may include one or more of thefollowing: a format of the response frame (e.g., whether the replyingframe is an NDP frame or a normal frame with a MAC body), whethersub-channel-selection-related-information is required in the responseframe, whether synchronization information is required in the responseframe, whether an uplink sounding frame or training sequence is requiredwith the ULR frame, whether link-adaptation-related-information isrequired in the ULR frame, or whether the multiple desired receiverstransmit the response frame simultaneously in the frequency, time andcode domains.

Sub-channel-selection-related-information may include, for example, therank or order of the sub-channels, the measurement (e.g., SINR or RSSIon each sub-channel), or the best and/or worst sub-channel(s).Synchronization information may include, for example, the transmitpower, link margin, timestamp or compressed timestamp, or carrierfrequency offset. With respect to whether an uplink sounding frame ortraining sequence is required with the ULR frame, this may allow the APto sound the channel of the STAs, and, thus, to schedule the uplink MUtransmissions accordingly. If multiple sounding frames are allowed, thissub-field may be used to indicate a specific sounding frame format.Information about whether the link adaptation related information isrequired in the ULR frame may be used by the AP to assign MCS for thecoming uplink MU transmissions. The design allows the AP to assign MCSfor STAs.

Simultaneous transmission in the frequency domain may mean that the STAstransmit response frames on their assigned sub-channels, which may notoverlap with each other. Simultaneous transmission in the time domainmay mean that the STAs transmit response frames on different time slots.The AP may or may not poll them before each uplink transmission.Simultaneous transmission in the code domain may mean that the STAs usethe same time-frequency resource to transmit the response frames.However, they may use pre-defined orthogonal sequences such that the APmay distinguish them at the receiver.

FIG. 22 illustrates a flow diagram of example HE MU procedures using theexample NDP MU control frame of FIG. 21 . Operations 2201-2210 aresimilar to operations 2001-2010 in FIG. 20 , respectively, except inoperation 2209 the STA may additionally check the ULR protocol field forpreparing corresponding information according thereto. The AP mayprepare and transmit the HE NDP MU-Poll frame after it acquires themedia and has traffic for multiple users, and STA may receive thispacket and begin packet detection using the L-STF and L-LTF fields inaccordance with FIG. 22 .

With respect to a third example NDP MU-Poll frame body, the frame bodymay be included in a SIG field of an NDP MAC PPDU, which may use thestructure given in the HE MAC PPDU shown in FIG. 9 .

FIG. 23 is a diagram of the third example of a NDP MU-Poll frame body2300. In the example illustrated in FIG. 23 , the NDP MU-RTS frame body2300 may allow the AP to poll any of the users such that the intendeduser of this frame may not be restricted by a group ID or a multicastID. Any STA that has uplink traffic that it intends to transmit viauplink MU transmissions may reply with a ULR frame upon reception ofthis frame. In this example, most of the subfields are similar to theexample shown in FIG. 19 , but the subfields may use a different numberof bits. Further, in this example, the Group ID/Multicast PAID subfieldmay not be included and a Contention ULR allowed subfield may beprovided, which may be used to indicate whethercontention-based-ULR-transmissions are allowed and, in an example, thetype of contention-based-ULR-transmissions permitted. For example, theULR may be transmitted simultaneously using different orthogonalsequences after an SIFS time later following this frame. Or the AP mayreserve a particular time slot for the STAs that intend to transmit inthe UL MU transmissions to compete and send ULR frames, etc.

FIG. 24 illustrates a flow diagram of example HE MU procedures using theexample NDP MU control frame of FIG. 23 . Operations 2401-2407 aresimilar to operations 2001-2007 in FIG. 20 , respectively. In addition,in operation 2408, the STA may determine whether it is associated withthe AP, and, if so, the STA may proceed to operation 2409. Otherwise,the STA proceeds to operation 2410 and checks the duration field andsets up its NAV accordingly.

In particular, the AP may prepare and transmit the HE NDP MU-Poll frameafter it acquires the media and has traffic for multiple users, and STAsmay receive this packet and begin packet detection using the L-STF andL-LTF fields. By decoding the L-SIG field, a STA may determine thelength of this transmission (2401). STA may continue decoding theHE-NDP-SIG field and may notice that this is an NDP MAC frame when theNDP indication field is set to 1 (2404).

The STA may revisit the NDP Mac Frame body subfield (2406). Here, theNDP Mac Frame Type and MU mode subfields may indicate the MU-Poll frameand the MU transmission mode (2407). By checking the AP address, the STAmay determine whether this frame is transmitted by an associated AP(2408). If the STA is associated with the AP, it may continue thedecoding procedure in operation 2409. Otherwise, the STA may determineit is not part of the transmission, and it may check the duration fieldand set up NAV accordingly (2410).

Upon confirming that a STA is associated with the AP (2408), STAs whoare associated with the AP and have data to transmit may take thisopportunity to send UL frames. In another words, the frame shown in FIG.23 is a type of broadcasted frame that is transmitted by the AP to allof associated STAs. Accordingly, it will be appreciated that allassociated STAs are also intended receivers, such that the STAs maycontend for one or more slots for an uplink transmission.

By checking the Contention ULR allowed field, the STA may determinewhether a contention-based-ULR-transmission-slot is scheduled after aSIFS time following the current frame (2409) and may check the trafficbuffer to determine whether it may perform a contention based ULRtransmission with the data waiting for transmission in the buffer(2411). If the STA determines that a contention based UL transmission isnot allowed in operation 2409, the STA may check the duration field andset up its NAV accordingly (2412).

With respect to a fourth example of a NDP MU-Poll frame body, the framebody may be included in a SIG field of an NDP MAC PPDU, which may usethe structure given in the example HE NDP PPDU shown in FIG. 10 , whereNDP-SIG-A and NDP-SIG-B fields may be used.

FIG. 25 is a diagram of the fourth example of a NDP MU-Poll frame body2500. In the example illustrated in FIG. 25 , the NDP frame body 2500 acontained in the NDP-SIG-A field may include an NDP MAC Frame Typesubfield, an MU mode subfield, an AP address/TA subfield, a Durationsubfield, a Synchronization subfield, a BW subfield, an NDP-SIG-Bpresent subfield and a Reserved subfield.

The NDP MAC Frame Type subfield may be used to indicate and/or identifythe HE NDP MU-Poll frame. The MU mode subfield may be used to indicateor identify the MU transmission mode (e.g., MU-MIMO, OFDMA, single user(SU) or time domain multi-user aggregation). In an alternative example,the MU mode subfield may be combined with the NDP MAC Frame Typesubfield. The AP address/TA subfield may be used to signal or providethe transmitter address. When the MU-Poll frame is transmitted by theAP, it may be used to signal or provide the AP address. The Durationsubfield may be used to signal or provide the duration of the TXOP.Unintended STAs may use the Duration subfield to set their NAV.

The Synchronization Info subfield may include time/frequency/powersynchronization-related-information transmitted from the AP to the STAs.Or the AP may use this subfield to require the STAs to respond withrequired time/frequency/power-synchronization-related-information. Thissubfield may be included in the NDP-SIG-A field (as shown in FIG. 15 ),and the synchronization information may be shared with all theSTAs/users. In an alternative example, this subfield may be included inthe NDP-SIG-B field and may include userspecific/STA-dedicated-synchronization-information.

The BW subfield may be used to indicate BW, which may be an operation BWof the AP, an acquired BW in the TXOP or the sub-channel BW (where basicsub-channel size may be varied per transmission). The NDP-SIG-B presentsubfield may be used to signal whether a NDP-SIG-B field follows theNDP-SIG-A field. The Reserved subfield may be reserved for future use.

The user/resource-dedicated-MAC-frame-body 2500 b included in theHE-NDP-SIG-B field may include a PAID subfield, a Response protocolsubfield and a Reserved subfield. The PAID subfield may include apartial AID or another possible ID that may be used to represent theSTA. The NDP-SIG-B field may be resource/user-dedicated, and, thus, thePAID field may be used to implicitly signal the resource allocation. Forexample, the NDP-SIG-B field transmitted on sub-channels k and n maycarry the same PAID. Then the user indicated by the PAID may beallocated to sub-channels k and n.

The ULR protocol subfield may be included in the NDP-SIG-B field and maycontain the user/STA-dedicated-response-protocol. In an alternativeexample, this subfield may be included in the NDP-SIG-A field, and theresponse protocol may be shared with all the STAs/users. This subfieldmay be similar to that defined in the second example HE NDP MU-Pollframe body embodiment. The Reserved subfield may be reserved for futureuse.

FIG. 26 illustrates a flow diagram of example HE MU procedures using theexample NDP MU control frame of FIG. 25 . Some operations 2601-2610 inFIG. 26 may be similar to operations 2001-2010 in FIG. 20 , with someexceptions related to the use of NDP SIG-A and NDP-SIG-B. For example,after determining that the frame is an NDP frame in 2604, the STA maycheck the AP address in the NDP SIG-A field to determine whether the STAis associated with the AP. If so, the STA proceeds to operation 2607,and, if not, the STA proceeds to operation 2608 and sets its NAV basedon the duration field. In operation 2607, the STA checks the STA ID inthe NDP SIG-B field to determine whether it is an intended recipient ofthe MU-transmission. If so, the STA proceeds to operation 2609, and, ifnot, the STA proceeds to operation 2601 and sets its NAV based on theduration field. In operation 2609, the STA checks its traffic buffer anddetermines whether it has traffic/data to transmit, and, if so, preparesthe responding frame to transmit to the AP.

In particular, the AP may prepare and transmit the HE NDP MU-Poll frameafter it acquires the media and has traffic for multiple users, and STAsmay receive this packet and begin packet detection using the L-STF andL-LTF fields. By decoding the L-SIG field, the STA may determine thelength of this transmission (2601). After determining that the length isless than a threshold (2602), the STA may continue decoding theHE-NDP-SIG-A field and may verify that this is an NDP MAC frame when theNDP indication field is set to 1 (2604). After confirming that the frameis an NDP frame, the STA may check the NDP MAC frame type subfield todetermine the type of frame. The STA may check the AP address anddetermine whether it is associated with the AP (2606). The STA may alsodetermine that the NDP-SIG-B field is present following the NDP SIG-Afield when the NDP SIG-B Present field is 1, and this operation may beperformed in conjunction with operation 2604 or 2606, or in betweenthose operations. STAs that are associated with the AP may continueanalyzing the NDP-SIG-B field by checking/reading the subfields therein(2607). STAs that are not associated with this AP may check the durationfield and set their NAV accordingly (2608). They may also check the BWfield to determine the operating sub-channels for the MU transmission.These operating sub-channels may be the sub-channels the AP acquired fortransmission and may be the same as or less than the total operationbandwidth announced by the AP. In this way, the OBSS STAs may set theirNAV on the utilized sub-channels and may be allowed to use the unusedsub-channel(s) when they became available.

The STAs associated with the AP may continue analyzing the NDP-SIG-Bfield (2607). Since NDP-SIG-B fields transmitted on differentsub-channels may be different, the STAs may need to decode all theNDP-SIG-B fields transmitted on all of the sub-channels. By checking thePAID field (or other possible identities) on each sub-channel, the STAmay determine whether it is a STA assigned to that sub-channel (2607)(i.e., the STA determines whether it is an intended recipient). A STAmay be assigned to multiple sub-channels. Thus, the STA may need todecode NDP SIG-B fields on all of the sub-channels. The STAs that areassigned to one or more sub-channels may check their traffic buffer andprepare the responding frames based on the information carried in boththe NDP-SIG-A and NDP-SIG-B fields (2609). The STAs that are notassigned any sub-channel may set their NAV accordingly (2610).

Examples of an NDP MU UL Schedule frame body are described below. An NDPMU UL Schedule frame may be used by an AP to reserve a UL MU TXOP andschedule a UL MU transmission. The NDP MU UL Schedule frame may use asimilar frame format as any of the NDP MU-RTS frame examples describedabove (e.g., see FIGS. 11, 13 and 15 ). In particular, any of the threeexample NDP MU-RTS frames may be applied to the NDP MU UL schedule framedirectly, although, in some examples, the NDP Mac Frame Type andsynchronization Info subfield may be different.

The NDP Mac Frame Type subfield may indicate that this is a NDP MU ULSchedule frame. The Synchronization Info subfield may include thesuggested synchronization information, which may include at least one ofa suggested transmit power, a suggested timing adjustment or a suggestedfrequency adjustment.

In an alternative example, the NDP MU UL Schedule frame may includeextra uplink control information, which may include a Suggested/assignedNsts subfield, a Suggested/assigned MCS subfield, a Suggested/assignedBW subfield, and a Maximum UL packet length subfield. TheSuggested/assigned Nsts subfield may be used to indicate the suggestedor assigned number of spatial time streams for each user. If the exampleNDP PPDU shown in FIG. 10 is used, this subfield may be carried in theNDP-SIG-B field. The Suggested/assigned MCS subfield may be used toindicate the suggested or assigned MCS for each user. If the example NDPPPDU shown in FIG. 10 is used, this subfield may be carried in theNDP-SIG-B field. The Suggested/assigned BW subfield may be used toindicate the suggested or assigned bandwidth for each user. This may beimplicitly signaled by a group ID. If the example NDP PPDU shown in FIG.10 is used, this subfield may be carried in the NDP-SIG-B fieldimplicitly or explicitly. The Maximum UL packet length subfield maycarry the maximum UL packet length. The AP may calculate the maximum ULpacket length according to the UL traffic information transmitted in ULRframes and assigned MCS/Nsts. The STA may use this subfield to pad theuplink packet such that they arrive at the AP aligned.

FIG. 27 illustrates a flow diagram of example HE MU procedures using aNDP MU UL schedule control frame. Some operations in FIG. 27 may besimilar to operations in FIG. 12 , and should be self-explanatory. Forexample, after determining that the frame is an NDP frame in 2704, theSTA may revisit the NDP SIG field (2706) and check the NDP MAC frametype field to determine the frame type (2707). Upon determining that theframe is a NDP MU UL schedule control frame in operation 2707, the STAmay decide to check/read the IDs in AP address, group ID and/or clusterID (not shown) fields to determine whether the STA is an intendedrecipient of the NDP MAC frame (2708). If yes, the STA proceeds tooperation 2709, and, if not, the STA proceeds to set its NAV based onthe duration field in operation 2710. In operation 2709, the STA mayprepare the UL data transmission and preform synchronization and set atransmission control protocol (TCP). Thereafter, the STA may use the MCSand Nsts assigned by the AP for the uplink traffic transmission (2711).

In particular, the AP may prepare the NDP MU UL Schedule frame followingother MU control frames, such as the NDP MU-Poll and the NDP ULRexchanges. Alternatively, the AP may acquire the media and transmit thisframe at a beginning of a UL MU TXOP. The STAs may check the AP addressfirst and determine whether they are associated with the AP (2708). TheSTAs that are not associated with this AP may set or update the NAVsetting accordingly (2710). If the BW field is carried in the HE NDP MUUL Schedule frame, the STAs may check their NAV on certain sub-channelsindicated by the BW field. The STAs that are associated with the AP maycontinue the decoding procedure to operation 2709.

The STAs may check the Group ID/Cluster field (2708). The STAs thatbelong to the group/cluster may prepare the uplink transmission (2709).They may use the synchronization suggested from the AP to adjust thepower, timing and frequency offset and set a TCP (2709). They may usethe MCS and Nsts assigned by the AP for the uplink traffic transmission(2711). They may use the Maximum UL packet length as guidance forpadding or truncating. The STAs that do not belong to the group orcluster may set or update their NAV accordingly (2710).

Examples of an NDP ULR frame body shown in FIG. 28 are described below.An NDP URL frame may be used by STA to signal or indicate the uplinktraffic and request a UL TXOP. In an example, the AP may poll the STAs,and the STAs may reply with ULR frames. In another example, the STAs maytransmit a ULR frame without polling from the AP (e.g., once everypredetermined time period).

FIG. 28 is a diagram of an example HE NDP ULR frame body, which may beincluded in a SIG field of an NDP MAC PPDU. The NDP MAC PPDU may use thestructure given in the example HE NDP MAC PPDU shown in FIG. 9 .

In the example illustrated in FIG. 28 , the NDP ULR MAC frame body fieldmay include an NDP MAC Frame Type subfield, an MU mode subfield, a PAIDsubfield, a Traffic Info subfield, a Preferred MCS/Nsts subfield, aDuration subfield, and a Reserved subfield.

The NDP MAC Frame Type subfield may be used to indicate or identify thatthis is an HE NDP ULR frame. The MU mode subfield may be used toindicate or identify the MU transmission mode (e.g., MU-MIMO, OFDMA, SUor time domain multi-user aggregation). In an alternative example, theMU mode subfield may be combined with the NDP MAC Frame Type subfield.The PAID subfield may be used to signal or provide the transmitteraddress. When the ULR frame is transmitted by a STA, it may be used tosignal or provide the STA address. The Traffic Info subfield may be usedto signal or provide the uplink traffic information, which may include,for example, length, priority, traffic category or access category.

The Preferred MCS/Nsts subfield may be used by the STA to indicate oridentify the preferred MCS and/or Nsts and the number of spatial timestreams. The Preferred sub-channel subfield may be used by the STA toindicate or identify the preferred sub-channel or resource allocation.In an alternative example, instead of indicating or identifying thepreferred sub-channel, this subfield may be used to indicate or providethe rank/order of the sub-channels or the detailed channel measurements,such as SINR or RSSI on each sub-channel.

The Duration subfield may be used to signal or provide the duration ofthe TXOP. Unintended STA may use this subfield to set their NAV. TheReserved subfield may be reserved for future use.

In another example, an HE NDP ULR frame may include additionalsubfields, such as a Synchronization Info subfield. The SynchronizationInfo subfield may includetime/frequency/power-synchronization-related-information transmittedfrom the STA to the AP. The STA may use this subfield to require the APto report time/frequency/power-synchronization-related-information.

The STA that has uplink traffic may transmit an NDP ULR frame when itacquires the media, or STAs that are polled by the AP may respond withan NDP ULR frame. On a condition that multiple STAs transmit NDP ULRframes simultaneously, the NDP ULR frames may be separated in the time,frequency, code or spatial domains.

FIG. 29 illustrates a flow diagram of example HE MU procedures using theexample NDP MU control frame of FIG. 28 . The STA may prepare the MU-ULRframe (2901), the STA may indicate NDP ULR frame in NDP Mac Frame Typefield (2902), the STA may include the transmitter ID in the PAID/TAfield (2903), the STA may indicate the preferred sub-channel andMCS/Nsts in the Sub-Channel Info and Preferred MCS/Nsts field (2904),the STA may indicate traffic length, priority, traffic category andaccess category in Traffic Info field (2905) and the STA may indicateTXOP duration in the Duration field (2906).

Upon receiving one or more NDP MAC ULR frames, the AP may detect all ofthe ULR frames and may use the collected preferred sub-channelsinformation and traffic information for clustering/grouping. The AP mayprepare an NDP UL MU Schedule frame to schedule an MU uplinktransmission. The AP may use the collected synchronization informationto suggest or set power, timing and frequency adjustment and may use thecollected channel state information to suggest or set MCS and Nsts forthe uplink transmission. Non-desired STAs may receive the NDP UL MUSchedule frame from the AP and may perform and update or set their NAVaccordingly.

The examples described above use a SIFS as the inter-frame spacing.However, other inter-frame spacing techniques (e.g., reduced inter-framespace (RIFS)) may be used. Further, although the solutions describedherein consider IEEE 802.11 specific protocols, it is understood thatthe solutions described herein are not restricted to this scenario andare also applicable to other wireless systems.

Analysis has been performed to compare the following three scenarios:baseline (single user transmission using the current version of IEEE802.11ac) (SU), UL OFDMA transmission with full MAC control frames(OFDMA), and UL OFDMA transmission with the example NDP MAC framesdescribed herein (NDP OFDMA). The assumptions for the analysis were thatthe AP is operating on an 80 MHz channel (for the SU case, the non APSTA is operating on the 80 MHz channel, and for the OFDMA case, fourusers are assumed and each has been assigned a 20 MHz sub-channel); twoMSDU packet sizes were used (1408 bytes (large packet); and 36 bytes(small packet)); and UL OFDMA channel access includes MU Poll, ULR, MUSchedule, Uplink OFDMA data, and ACK frames. The analysis was also basedon PHY layer simulations on Channel B, where the AP has 8 antennas andthe STA have one antenna. However, it will be appreciate that thefeatures and techniques disclosed herein may be applied to otherscenarios without departing from the concepts disclosed herein.

FIG. 30 is a graph showing the result of the analysis comparing thebaseline, UL OFDMA transmission for full MAC control frames and UL OFDMAtransmission with the example NDP MAC frames described herein for largepackets.

FIG. 31 is a graph showing the result of the analysis comparing thebaseline, UL OFDMA transmission for full MAC control frames and UL OFDMAtransmission with the example NDP MAC frames described herein for smallpackets.

The results of the analysis show that throughput improvement issignificant using the OFDMA NDP scheme.

As described in detail above, UL MU transmissions involve multiple userstransmitting simultaneously. Exchanging traffic information,synchronizing among the multiple users, and allocating resources mayneed to be performed before the uplink data transmission. Thus, extracontrol frames may be required for UL MU transmissions. For example, anAP may need to poll the multiple STAs to determine whether the STAs haveuplink traffic to transmit. Non-AP-STAs may request an uplinktransmission opportunity from an AP. An AP may need to send a frame toschedule and trigger the UL MU transmission so that the multiple STAsmay synchronize and prepare the uplink data transmission. An AP and STAsmay need to exchange pre-correction parameters for UL MUsynchronization. All of the above exemplary frame exchanges may beconsidered to be extra overhead and may cause the reduction of systemthroughput. In the examples described below, methods for evaluating theperformance of the UL MU transmissions are described, which may be usedto aid in the formulation of design criteria for any of the UL MUapparatuses, systems and methods described herein.

FIG. 32 is a diagram of an example abstracted model for SU transmissionsand UL MU transmissions. In the example illustrated in FIG. 32 , SUtransmissions and UL MU transmissions are considered as part of theframework for analyzing how much of the overhead for UL MU controlframes may be acceptable by comparing overhead for UL MU transmissionswith the overhead for SU transmissions. In FIG. 32 and the equationsthat follow, T_(con) is a contention duration, T_(p) is a preambleduration, T_(d) ^(SU) is an SU data packet duration, T_(d) ^(MU) is anMU data packet duration, T_(c) is a UL MU control frame duration(including a SIFS) and T_(ack) is an acknowledgement frame duration(including a SIFS).

For SU transmissions, a STA may transmit a packet to another STA using aconventional CSMA/CA mechanism. The STA may compete for and acquire thewireless medium and then send a PPDU, which may include a preamble and aMAC frame. If the receiving STA decodes the packet successfully, it maysend an acknowledgement frame to the first STA a SIFS time afterreception of the data packet.

For UL MU transmissions, an AP or non-AP STA may compete for and acquirethe wireless medium, and the AP and STAs may exchange control frames.The STAs may then begin an UL MU transmission to the AP. The AP, afterdecoding the packets, may transmit acknowledgement frames to the STAs.In the examples described herein, an OFDMA scheme is used as an exampleto perform overhead analysis for UL MU transmissions. However, designsand analyses for UL MU apparatuses, systems and methods may be adaptedfor any type of scheme.

In an example, in order to achieve a targeted throughput gain G, where

${\frac{{Throughtput}_{MU}}{{Throughput}_{SU}} \geq G},$

the MU control frame may be designed in such a way that the totalcontrol frame duration satisfies:

$\begin{matrix}{T_{c} < {\frac{( {T_{con} + T_{p} + T_{ack}} )( {N_{U} - G} )}{G} + {\frac{( {1 - G} )}{G}T_{d}^{MU}}}} & ( {{Equation}1} )\end{matrix}$

Based on Equation 1, the baseline requirement when G=1 is:

T _(c)≤(T _(con) +T _(p) +T _(ack))(N _(U)−1),

where N_(U) is the number of users in the UL MU transmission.

Assuming that MU and SU transmissions have the same contention period,that packet size is fixed for both SU and MU transmissions, and that theMCS level is fixed for both SU and MU transmissions, the TXOP durationof the MU transmission is (where D_(MU) represents the information bitstransmitted by a UL STA, R_(MU) represents the MCS rate by one UL STA,D_(SU) represents the information bits transmitted by the SUtransmission, R_(SU) represents the MCS rate used in the SUtransmission, N_(d) represents the number of data tones and T_(sym)represents the OFDM symbol duration including CP):

T _(MU) =T _(con) +T _(c) +T _(p) +T _(d) ^(MU) +T _(ack); and

the TXOP duration of the SU transmission is:

${{T_{SU} = {T_{con} + T_{p} + T_{d}^{SU} + T_{ack}}},{{where}:}}{T_{d}^{MU} = {{\lceil \frac{D_{MU} \cdot N_{U}}{R_{MU} \cdot N_{d}} \rceil T_{sym}} \approx {\frac{D_{MU} \cdot N_{U}}{R_{MU} \cdot N_{d}}T_{sym}{and}}}}{T_{d}^{SU} = {{\lceil \frac{D_{SU}}{R_{SU} \cdot N_{d}} \rceil T_{sym}} \approx {\frac{D_{SU} \cdot T_{sym}}{R_{SU} \cdot N_{d}}.}}}$

Based on the above, the maximum throughput for the MU transmission maybe expressed as:

$\begin{matrix}{{Th}_{MU} = {\frac{N_{U} \cdot D_{MU}}{T_{MU}} = \frac{N_{U} \cdot D_{MU}}{T_{con} + T_{c} + T_{p} + T_{d}^{MU} + T_{ack}}}} \\{\approx \frac{N_{U} \cdot D_{MU}}{T_{con} + T_{c} + T_{p} + {\frac{D_{MU} \cdot N_{u}}{R_{MU} \cdot N_{d}}T_{sym}} + T_{ack}}} \\{= \frac{N_{U} \cdot D_{MU}}{( {T_{con} + T_{p} + T_{ack}} ) + {\frac{D_{MU} \cdot N_{u}}{R_{MU} \cdot N_{d}}T_{sym}} + T_{c}}}\end{matrix}$

The throughput for the SU transmission may be expressed as:

$\begin{matrix}{{Th}_{SU} = {\frac{D_{SU}}{T_{SU}} = \frac{D_{SU}}{T_{con} + T_{p} + T_{d}^{SU} + T_{ack}}}} \\{\approx \frac{D_{SU}}{T_{con} + T_{p} + \frac{D_{SU} \cdot T_{sym}}{R_{SU} \cdot N_{d}} + T_{ack}}} \\{= \frac{D_{SU}}{( {T_{con} + T_{p} + T_{ack}} ) + \frac{D_{SU} \cdot T_{sym}}{R_{SU} \cdot N_{d}}}}\end{matrix}$

Based on the assumptions described above, R_(MU)=R_(SU)=R (SU and MUtransmissions have the same MCS). If the common part of the equationsfor the throughput for the MU and SU transmissions(T_(con)+T_(p)+T_(ack))RN_(d) is denoted as A, then the ratio of thethroughput may be given by:

$\frac{{Th}_{MU}}{{Th}_{SU}} = \frac{\frac{N_{U}D_{MU}{RN}_{d}}{A + {N_{U}D_{MU}T_{sym}} + {T_{c}{RN}_{d}}}}{\frac{D_{SU}{RN}_{d}}{A + {D_{SU}T_{sym}}}}$

If a further assumption is made that D_(MU)=D_(SU)=D (the packet sizesfor each STA are the same), then:

$\begin{matrix}{\frac{{Th}_{MU}}{{Th}_{SU}} = \frac{\frac{N_{U}}{A + {N_{U}{DT}_{sym}} + {T_{c}{RN}_{d}}}}{\frac{1}{A + {DT}_{sym}}}} \\{= \frac{( {A + {DT}_{sym}} )N_{U}}{A + {N_{U}{DT}_{sym}} + {T_{c}{RN}_{d}}}}\end{matrix}$

MU transmissions may be considered to be desirable when the throughputratio is expected to be greater than a certain threshold G (or G=1):

${\frac{{Th}_{MU}}{{Th}_{SU}} = {\frac{( {A + {DT}_{sym}} )N_{U}}{A + {N_{U}{DT}_{sym}} + {T_{c}{RN}_{d}}} > G}}{{Then}:}{{( {A + {DT}_{sym}} )N_{U}} > {G( {A + {N_{U}{DT}_{sym}} + {T_{c}{RN}_{d}}} )}}$

In order to achieve a 100*(G−1) percent throughput gain, the duration ofUL MU control frames should satisfy:

${T_{c} < \frac{{A( {N_{U} - G} )} + {( {1 - G} ){DT}_{sym}N_{U}}}{{CRN}_{d}}} = {\frac{{( {T_{con} + T_{p} + T_{ack}} ){{RN}_{d}( {N_{U} - G} )}} + {( {1 - G} ){DT}_{sym}N_{U}}}{{GRN}_{d}} = {\frac{( {T_{con} + T_{p} + T_{ack}} )( {N_{U} - G} )}{G} + \frac{( {1 - G} ){DT}_{sym}N_{U}}{{GRN}_{d}}}}$

DT_(sym)N_(U)/RN_(d) represents the duration of the data body for the MUtransmission, which is equivalent to T_(d) ^(MU). Given this, theequation presented above for a UL MU control frame duration T_(c) may besimplified as:

$T_{c} < {\frac{( {T_{con} + T_{p} + T_{ack}} )( {N_{U} - G} )}{G} + {\frac{( {1 - G} )}{G}T_{d}^{MU}}}$

And the baseline requirement may be expressed as G+1 or:

T _(c)<(T _(con) +T _(p) +T _(ack))(N _(U)−1)

To incorporate the above analysis into an IEEE 802.11 WiFi system, theassumptions may be adapted as provided in Table 1 below. The assumptionsprovided in Table 1 take the latest IEEE 802.11 development intoconsideration.

TABLE 1 Notation Description Value T_(con) Contention duration 27 μs (3time slot) T_(p) Preamble duration 48 μs T_(ack) Acknowledgementduration 96 μs (BA + SIFS) N_(U) # of users 4/8 T_(sym) OFDM symbolduration 16 μs (including CP) N_(d) # of data sub-carriers 234

FIG. 33 is a graph representing example design requirements fordifferent targeted gains for UL MU transmissions involving 4 OFDMAusers. FIG. 34 is a graph representing example design requirements fordifferent targeted gains for UL MU transmissions involving 8 OFDMAusers. The examples illustrated in FIGS. 33 and 34 show the curves ofmaximum allowed control frame duration versus OFDM data packet size withvarious given targeted throughput gains.

In the examples represented by FIGS. 33 and 34 , when the targetedthroughput threshold G is set to 1, which means that the throughput ofMU transmissions is expected to be as efficient as that of SUtransmissions, the maximum allowed control frame duration is not afunction of the OFDM data packet size; the OFDM data packet size is afunction of packet size (in bits), MCS rate, and number of sub-carriersper OFDM symbol per user. The maximum allowed control frame duration is513 μs and 1197 μs for 4 user and 8 user OFDMA transmissions,respectively. If the design target G, the targeted throughput gainthreshold for MU, is increased, the maximum allowed control frameduration may decrease significantly.

Further, in the examples represented by FIGS. 33 and 34 , with G greaterthan 1, the maximum allowed control frame duration, T_(c), is a functionof the OFDM data packet size. For example, with 4 user OFDMA, themaximum allowed control frame duration is 280 μs, 163 μs and 46 μs whenG is set to 1.5, 2 and 3, respectively, if the MU data packet iscontained in 1 OFDM symbol. When a larger packet is considered (e.g., 20OFDM symbols for an MU data transmission), the maximum allowed controlframe duration may be 178 μs if 1.5 time MU throughput gain is targeted.If 2 time MU throughput gain is expected, then the entire controloverhead for UL MU transmission may need to be limited within 11 μs. Andit may not be possible to achieve 3 time MU throughput gain with a 4user OFDMA transmission and 20 MU data symbols.

For 8 OFDMA transmissions, the MU transmission may be more efficientsince more users may share the same contention period and preambleduration. Moreover, the acknowledgment signaling may be simultaneous.Thus, the system may tolerate longer control frame overhead. Asillustrated in FIG. 34 , for example, with a small MU packet size (e.g.,1 OFDM symbol), the maximum allowed control frame duration may be 736μs, 505 μs and 274 μs when G is set to 1.5, 2 and 3, respectively. Witha larger MU packet size (e.g., 20 OFDM symbols), the maximum allowedcontrol frame duration may be 634 μs, 353 μs and 72 μs when G is set to1.5, 2 and 3, respectively.

FIG. 35 is a graph representing a design requirement for UL MU controlframes with 4 OFDMA users when data symbol length is fixed.

FIG. 36 is a graph representing a design requirement for UL MU controlframes with 8 OFDMA users when data symbol length is fixed.

Although features and elements are described above in particularcombinations, one of ordinary skill in the art will appreciate that eachfeature or element can be used alone or in any combination with theother features and elements. In addition, the methods described hereinmay be implemented in a computer program, software, or firmwareincorporated in a computer-readable medium for execution by a computeror processor. Examples of computer-readable media include electronicsignals (transmitted over wired or wireless connections) andcomputer-readable storage media. Examples of computer-readable storagemedia include, but are not limited to, a read only memory (ROM), arandom access memory (RAM), a register, cache memory, semiconductormemory devices, magnetic media such as internal hard disks and removabledisks, magneto-optical media, and optical media such as CD-ROM disks,and digital versatile disks (DVDs). A processor in association withsoftware may be used to implement a radio frequency transceiver for usein a WTRU, UE, STA, terminal, base station, RNC, or any host computer.

What is claimed is:
 1. A method for use in a station (STA), the methodcomprising: receiving, from an access point (AP), a null data packet(NDP) multi-user (MU) poll frame that includes an address of the AP andan indication of a reserved resource for multi-user (MU) transmission;and transmitting, based on the address of the AP that the STA isassociated with and the reserved resource, an NDP response frame as theMU transmission when the STA has uplink data to transmit in a trafficbuffer of the STA.
 2. The method of claim 1, wherein an interframe spacebetween the response frame and the NDP MU poll is a short interframespace (SIFS).
 3. The method of claim 2, wherein the reserved resource isa contention-based uplink request frame transmission slot scheduledafter the SIFS.
 4. A station (STA) comprising: a receiver configured toreceive, from an access point (AP), a null data packet (NDP) multi-user(MU) poll frame that includes an address of the AP and an indication ofa reserved resource for multi-user (MU) transmission; and a transmitterconfigured to transmit, based on the address of the AP that the STA isassociated with and the reserved resource, an NDP response frame as theMU transmission when the STA has uplink data to transmit in a trafficbuffer of the STA.
 5. The STA of claim 4, wherein an interframe spacebetween the response frame and the NDP MU poll is a short interframespace (SIFS).
 6. The STA of claim 5, wherein the reserved resource is acontention-based uplink request frame transmission slot scheduled afterthe SIFS.
 7. A access point (AP) comprising: a transmitter configured totransmit, to a station (STA), a null data packet (NDP) multi-user (MU)poll frame that includes an address of the AP and an indication of areserved resource for multi-user (MU) transmission; and a receiverconfigured to received, from the STA, based on the address of the APthat the STA is associated with and the reserved resource, an NDPresponse frame as the MU transmission when the STA has uplink data totransmit in a traffic buffer of the STA.
 8. The AP of claim 7, whereinan interframe space between the response frame and the NDP MU poll is ashort interframe space (SIFS).
 9. The AP of claim 7, wherein thereserved resource is a contention-based uplink request frametransmission slot scheduled after the SIFS.